Effect of breast-feeding patterns intervals

Effect

of

_{breast-feeding}

_patterns

on

human

birth

intervals

P. W.

Howie

and A.

S.

_McNeilly

M.R.C. Unit

_of

_Reproductive

_Biology,

_University

_{of Edinburgh,}

Centre

Jor Reproductive

Biology,

37 ChalmersStreet,

_Edinburgh

EH3

9EW,

U.K.

An

_adequate

inter-birth interval is ofgreat

_importance

because it enablesamothertorecoverher

physical

and emotional

_strength

between

_pregnancies

andconfersuponthe child

advantages

of betterhealth and

_{development (Morley,}

1977).

Breast

_feeding

is the

naturally

evolved method of

ensuring

an

adequate

inter-birth interval but the

contraceptive

effect of breast

feeding

has been

largely

dismissed in

_developed

countriesonthe

grounds

that it is anunreliablemethod of

family

planning

for individual mothers

(Kamal

et

_al.,

_1969).

The use of artificial

contraception

varies very

_widely

in different

countries,

being

much

_higher

in

_developed

nations than in _{the poorer}

developing

countries

_{(Text-fig. 1).}

Wheretheuseofartificial

contraceptives

is

low,

breast

feeding

is themost

_widely

used method of birth

_spacing

andassumes

_{major demographic importance.}

It is

_important,

therefore,

that the factors

_controlling

lactational

_infertility

should be understood so

that

_guidelines

canbe

developed

whichwillallow motherstomaximize the

_{birth-spacing}

effect of breast

_feeding

to their own

advantage.

In

developed

countries,

few mothers choose to

_rely

on

breast

_feeding

for

_{family planning although}

an

increasing minority

mayfind breast

feeding

tobe

an attractive method of

_spacing

their

families,

_{thereby avoiding}

the

_potentially

adverse side-effects of

_currently

available

_{contraceptive}

methods. Abetter

_{understanding}

ofhow breast

feeding

mediates its

_{birth-spacing}

effect may lead to the

_development

of new

contraceptive

methods which will try to imitate this

naturally

evolved method of

_fertility

control

_(McNeilly,

1979).

Developed countries Middle Income countries Poor countries USA UK JAPAN POLAND MEXICO PERU DOMINICAN REPUBLIC JORDAN INDIA PAKISTAN GHANA ZAMBIA =1 =1 ) 20 40 60 %_{Contraceptive}users 80 100

Text-fig.

1.

_{Contraceptive}

usage

by

married women aged 15-44 years in differentcountriesby

economicstatus.Source:

_Population

Reference Bureau Inc.

_Washington

D.C.,U.S.A.

*

Reprintrequeststo:Dr A.S.McNeilly.

t

Present address:_Departmentof Obstetrics &Gynaecology,NinewellsHospitaland MedicalSchool,University

ofDundee,Dundee,U.K.

0022-4251/82/040545-13S02.00/0

This paper will describe the methods which have been used to

_investigate

lactational

infertility

and discusshowdifferent

breast-feeding

patternsinfluencehumanbirth intervals.

Methodsof

assessing

lactational

infertility

Lactational

_infertility

can _{be measured} in _{three different ways:}

(1) by

_{the duration of the}

interbirth

interval,

(2) by

the duration of lactational amenorrhoea and

_{(3) by}

the return of ovulation. These methods presentdifferent

_problems

of

_{interpretation}

anda

complete picture

of

lactational

_infertility

can

only

be achieved

by

considering

all the information which has been

gathered

from these differentsources.

Interbirth interval. The ultimate test of

_fertility

is pregnancy and several

_reports

have demonstrated that breast

feeding

increases the interval between

_pregnancies

(for

summary, see van

Ginneken,

1977).

For

example,

twostudies

compared

the timeto next

_conception

in

_nursing

and

_non-nursing

mothers from Alaskan Eskimo

(Berman,

Hanson &

Hellman,

1972)

and rural Indian

_{populations (Potter,}

_New,

_Wyon

&

_Gordon,

_{1965). Despite}

the wide differences in climate and

culture,

the

conception

rates were similar in the two

_populations

and

_conception

occurred sooner in the

non-lactating

than

lactating

mothers

(Text-fig.

2). Considering

the time

until 50% of the mothers conceived

again,

_{breast-feeding}

conferred an additional

fertility

protection

of 14 months in the Indian women and 10months in the Eskimo women;

assuming

that these intervals

_repeated

themselves between successive

pregnancies,

this would meanthat

non-nursing

women would have almost double the number of children than the breast

feeding

women overthesametime

period.

^ Non-lactating --Lactating O Eskimo •RuralIndian 6 12 18

Months post partum

24

Text-fig.

2. Cumulative conception rates since _{last pregnancy in}

_lactating

and non-lactating

mothers. Data forEskimos fromBermanetal

_(1972),

Indianruralfrom Potteretal.(1965).

Rosa

₍₁₉₇₅₎

has

_attempted

to

_quantify

the

contraceptive

effect of breast

_feeding

in

developing

countries and has

_compared

its contribution to

_fertility

protection

with that of

artificial

_{contraceptives.}

_Assuming

additional

_{fertility protection}

of 8 months in rural mothers and of4 monthsin urban

mothers,

Rosa

₍₁₉₇₅₎

estimated

that,

in thecourse of 1 year, breast

feeding

contributed over 31 IO6

couple

_yearsof

_{contraceptive}

protection; by comparison,

_the

known sales of artificial

_{contraceptives}

contributed 24 IO6

_couple

years of

fertility protection

overthesametime

period.

Knodel

(1977)

has

pointed

outthat the

_demographic

consequencesof

breast

_feeding

are

complex

because the

contraceptive

effects of breast

feeding

on

population

growth

are

reduced,

at least to some extent,

by

the lower

_mortality

rates among breast fed

babies. There can be no

doubt, however,

_{that breast}

_feeding

_has

_{profound implications}

_in

Despite

the clear evidence that breast

_feeding

is associated with

_prolonged

interbirth

intervals,

itcannotbe assumed that breast

feeding

perseis

directly

responsible

for this effect. In many

cultures,

_particularly

in

Africa,

sexual taboos are

_imposed

_on

nursing

_{mothers and}

reduced

_frequency

ofintercourse could

explain,

at leastin _part, the

_{fertility-inhibiting}

effect of breast

_{feeding. Contraceptive}

practices during

lactation could also influence the interbirth interval and the use of coitus

interruptus,

for

example,

cannot be monitored on the basis of

contraceptive marketing figures.

An

_example

of how behavioural factors can influence the

interbirth interval was demonstrated

by

Chen, Ahmed,

Gesche &

Mosley (1974)

_during

their

detailed

_prospective

study

in

Bangladesh.

_They

found thatthe

_conception

rates after thereturn

ofpost-partum menses werelowerinfishermens' wives than in farmers'

wives,

probably

because

thefishermenwereabsent from home for

longer periods.

Itis

essential, therefore,

toknow what behavioural variables

_might

influence the interbirth interval before the

_{epidemiological}

evidence ofmore

prolonged

birth

spacing

canbe

directly

attributedtobreast

feeding

itself.

Lactational amenorrhoea. Thereturn of menstruationpost partum has been used in many

studies as an indirect index of resumed ovulation

(see

van

Ginneken,

1977).

This method is

convenient because it is easy tomeasure andcanbe

applied

to

large populations. Many

studies have shown thattheduration ofpost-partumamenorrhoea is

longer

in

_nursing

than

non-nursing

mothers

_(for

summary, see

Buchanan,

1975).

In

_non-nursing

mothers,

the duration of post-partum amenorrhoeaaverages about 3

months,

but among

_nursing

mothers it maylast for

more than 2 years. It is also clear that

fertility

is

markedly

reduced

during

the

period

of

lactational amenorrhoea. Chen et al

(1974)

calculated

that,

during

18 months oflactational amenorrhoea in

Bangladesh,

the pregnancy rate was less than 5 per 100 women years of

exposure which

compared

well with many artificial

_{contraceptive}

methods. The duration of lactational amenorrhoea is much

longer

in rural than in urban communities

(van Ginneken,

1977)

because rural mothers breast feedmore

intensively

andfora

longer

time.

Much valuable information hasbeen

_gathered

from the

study

oflactational amenorrhoea but its

_validity

_depends

upon the

_assumption

that the

_capacity

of breast

feeding

to _prevent pregnancy is limited to the duration of lactational amenorrhoea. It _{is well known that breast}

feeding

does not _{postpone pregnancy}

_indefinitely

and 2-10% ofmothers conceive

_during

the

period

of lactational amenorrhoea

(Badraoui

&

Hefnawi,

1979).

There is also evidence

(see

below)

that the

_fecundity

of breast

feeding

womendoes not return tonormal after the returnof

mensespost partum. It

is, therefore,

desirable to have information from studies which

_directly

measurethe

resumption

of ovulation

during

the_post-partum

period.

Detection

_of

ovulation. Most studies which have

attempted

todefine the

timing

ofovulation after childbirth have used endometrial

biopsy (Lass,

Smelser &

_{Kurzrok, 1938;}

_Topkins,

_1943;

Udesky,

1950;

El-Minawi &

_Foda,

1971),

basal

_body

_temperature

_{(Sharman, 1951; Cronin,}

1968),

cervicalmucus or

vaginal

cytology (Perez,

Vela,

Masnick&

Potter,

1972)

as markers of

ovulation but these methods present

_problems

of

_{interpretation. During}

_lactation,

the

_histology

of theendometrium mayshow

_inadequate

co-ordination ofmaturation

_signs

characteristic of the normal menstrual

_{cycle, making}

it difficult to determine whether ovulation has _occurred

(El-Minawi

&

Foda,

1972).

Ideally,

endometrial

_biopsies

should be taken in the

_{pre-menstrual}

phase

and,

in the absence of

regular

menstrual

_cycles,

the correct

_timing

of

_biopsies

can be

difficult to achieve.

_Biopsies

taken on the first

day

of

bleeding,

as

happened

in several

studies,

maybe unreliable markers of ovulation.

_Temperature

charts

_during

lactationmay showamuch shorter

_plateau

in the

_{pre-menstrual phase (Cronin, 1968) making}

_{precise interpretation}

difficult.

As an alternative to these

methods,

the use of

plasma

or

urinary

steroid concentrations

provides

objective

evidence ofovulation and enables a

quantitative

estimate ofmenstrual

_cycle

adequacy.

Rolland,

Lequin,

Schellekens & de

Jong

(1975)

used

_plasma

steroid levels to show that ovulation returned more

quickly

in mothers who discontinued breast

feeding early

_in the

puerperium

but the studies were not continued

beyond

100

days

post partum.

Urinary

total oestrogen and

pregnanediol

excretion can _{be used to monitor} ovarian follicular

_activity

and

ovulation

_(McNeilly,

Howie &

Houston,

1980)

and thisnon-invasive method has enabled us to

monitor 10

bottle-feeding

and 27

_{breast-feeding}

mothersfrom

delivery

untilfirstovulation.

1000r

500 -—

>

4 6 8 10 12 14 16 Weeksafterdelivery

Text-fig.3. Return of ovarian

_{activity (urinary}

total _oestrogens >10

_pg/24

_h)

and ovulation

(urinary pregnanediol

>1

_mg/24

h)inthe

_{early puerperium}

inabottle

feeding

mother.

.E o CD o 2^ ( TJ E 150 100 50 Solidfood 6000 r8 „ 6

_J-g

™ 2 w_g-S 4 6 8 1012141618202224262830323436384042444648505254

Weeks afterdelivery

Text-fig.

4.

_Delayed

return of_post-partum ovarian

_activity

and ovulation in a

_{breast-feeding}

The

_inhibitory

effects of breast

_feeding

are illustrated

by

the _pattern of endocrine events

leading

tothe

_resumption

of ovulationina

typical

bottle

feeding

(Text-fig. 3)

anda

typical

breast

feeding (Text-fig.

4)

mother. Inthe

_{bottle-feeding}

mother,

basal

prolactin

levels had returned to

the non-pregnant range within 4 weeks post partum and this was followed

by

an

early

resumption

of ovarian follicular

_activity

(total

_urinary

oestrogens > 10

µg/24

h)

andmenstrua¬

tion. Ovulation

_(urinary

_pregnanediol

> 1

_mg/24

_h)

did not occur

during

the first

cycle

but

resumed in the second and third

_cycles.

In the

breast-feeding

mother,

basal

_prolactin

levels fell

_{progressively}

as

suckling

duration was reduced but remained above the non-pregnant range until the cessation of breast

_feeding

at 40 weeks _{post partum.} Ovarian

_activity

and ovulation were

suppressed

until 44 weeks _{post partum} when the first

anovulatory cycle

was followed

_by

menstruation at 47 weeks. After the first post-partum

cycle,

there was an

interval of 7 weeks before the next menstruation which was followed

by

a normal

ovulatory

cycle.

Considering

the time of first ovulation in the total group of 10

_{bottle-feeding}

and 27

breast-feeding

mothers,

the bottle feeders ovulated between 6 and 15 weeks post partum

compared

with 15-68 weeksinthe breast feeders. This

finding

is consistent with

previous

reports

(Udesky,

1950; Sharman, 1951; Cronin, 1968;

Perez et

al,

1972)

and indicates that a

major

part of the

_{antifertility}

effect of breast

feeding

can be attributed to the inhibition of ovarian

follicular

_development

andovulation.

Components

of theinterbirth interval

The interbirth interval consists of three

phases,

the

_phase

of lactational

amenorrhoea,

the

menstruating

interval

(which

is the interval between thereturn ofpost-partum menstruation and

next

_conception)

and the

length

of

_gestation

itself.

Only

the

_period

of

gestation

is

relatively fixed,

the durations of lactational amenorrhoea andthe

_menstruating

interval

varying widely

between

populations

and between individuals within these

_populations.

It

_is,

_therefore,

_important

to

consider the

timing

and

_frequency

of ovulations

_during

lactational amenorrhoea and

during

the

menstruating

interval.

Ovulation

_during

lactational amenorrhoea. As

_previously

_discussed,

_fertility

is

_{substantially}

reduced

during

the

_phase

of lactational amenorrhoea butbetween2 and 10% of

_nursing

mothers conceive before first post-partum menstruation. This is an

important practical point

because it means that the return of menstruation cannot be used as an indication of when to resume

contraception.

Using

endometrial

_biopsy

as a marker of

ovulation,

Udesky (1950) reported

thatovulation

during

lactationwasfollowed either

by

menses or

by

pregnancy.This

finding

has been

supported

by

our own studies

(Howie,

McNeilly,

Houston,

Cook &

Boyle, 1981)

and indicates that recurrentovulationsdonottake

_place

throughout

the

phase

of lactational amenorrhoea. There is

some

dispute

about the

frequency

of ovulation in the

cycle

before the end of lactational

amenorrhoea,

the estimates

varying

from 14%

_(Udesky,

1950),

23%

(Cronin, 1968)

and 33%

(Howie

et

al,

1981)

to 75%

(Perez

et

al,

1972).

The different estimates of ovulation

frequency

during

lactational amenorrhoeamay be

partly explained by

the differentmethodsusedtoassess

ovulation but are more

likely

to be due to the different

suckling

patterns ofthe

_populations

studied. It has been shown that the

_longer

that the firstmenses is

delayed during

lactation,

the more

_likely

_isthe_first

_cycle

_tobe

ovulatory (Perez

et

_{al, 1972;}

Howieet

al,

1981).

The

impact

of different

_suckling

patternsuponpost-partumovulation is discussed below.

Ovulation

_during

the

_menstruating

interval. There is less informationaboutthe

_frequency

of ovulation in breast

feeding

mothers who have resumed menstruation and it has been

_suggested

that the

_capacity

of

prolonged

breast

_feeding

to

_prevent

pregnancy is limited tothe

period

of

during

the

_menstruating

interval. Chenetal

(1974)

studied the

_conception

rates afterthereturn

of

_post-partum

mensesin

nursing

mothers and found that

they

weremuch lower than would be

expected

in a

non-nursing

group ofwomen

(Tietze,

1968)

who were not

using contraception

(Text-fig.

5).

Similarly,

Potter et

al,

1965)

found pregnancy rates of 22 and 32% in

_nursing

mothers at 3 and 6 months after first menses

compared

with

corresponding figures

of 39 and

47% in mothers who

experienced

a neonatal death.

During

_the

_menstruating

interval,

_the

frequency

of

_{anovulatory cycles}

increased,

_being

estimated at55%

(Lass

et

al,

₁₉₃₈₎

and 42%

(Howie

et

al,

1981).

Reduced

_fecundity

amongst

nursing

mothers is further

_{supported by}

the increased intervals between menstrual

_{periods, compared}

with

cycles

in

non-nursing

mothers

(Sharman,

1951;

Berman et

al,

1972;

Howie et

al,

_1981),

which suggests a disturbance of

normal

_{rhythms during}

lactation.

12 6

Months

Text-fig.

5.

_Conception

rates in (#) nursing mothers after the return of_post-partum menses

(Chen

etal, 1974)and in

_{(o) non-nursing}

womenusingno

_{contraception (Tietze, 1968).}

Using plasma

steroid concentrations as a marker of

ovulation,

Duchen &

McNeilly (1980)

foundalowerincidenceof

ovulatory cycles during

lactation than would be

expected

in anormal

population.

An

_example

of an individual mother who hadrecurrent

anovulatory cycles

_during

lactation is shown in

_Text-fig.

6. After the introduction of solid

food,

basal

prolactin

levels

OÍ c >. coro ;~ TJ -· -* c-cn -o E 100r 50 Solid food

IMllríTfr-

»I · 1 )

<*&§

3000r 2 4 6 8 1012141618202224262830323436384042444648505254

Weeks afterdelivery

returned tothe pregnant range and there were 5

anovulatory cycles (urinary pregnanediol

_<1

mg/24

h)

before ovulation resumed after

_{complete weaning.}

We have studied the levels of

urinary

steroid excretion in 54

_{cycles during}

lactation and

_compared

them with the levels in 30

cycles

after lactation and 27

_cycles

innon-pregnant controls

_(Text-fig.

7).

_During

lactation,

the

mean

(±s.e.m.)

level of

urinary pregnanediol

in the luteal

phase

were 0·93 ± 0-09

mg/24

h

which was

significantly

lower than the mean level of 1-62 ± 0-15

mg/24

h in

cycles

after

lactation and 2· 13 ± 0-83

mg/24

h in thenon-pregnantcontrols.These results

suggested

a

high

incidence of

_cycles

which were _either anovular or characterized

_{by inadequate}

_luteal

phases.

Levels of total

_urinary

oestrogenexcretion

_(calculated

asthemeanof the4levels

throughout

the

cycle)

were 10-3 ± 1-0

µg/24

h in

cycles

during lactation,

12-2 ± 1-3

µg/24

h in

cycles

after

lactation and 14-1 ± 1-7

_µg/24

h in

_cycles

fromnon-pregnantcontrols. Thiswas_{consistent with}

the

_hypothesis

that the defective luteal function

_might

have its

_origins

in abnormal follicular

development (McNeilly

et

_al,

_1980).

3-1 _{Menses œ.}

(b)

4 -3 -2 -1 O

Weeksbeforemenses

(C)

Text-fig. 7. Excretion of

_urinary

total _oestrogen and

_pregnanediol

in menstrual

_cycles

(a)

during

lactation

_(n

=

54), (b)

after lactation

(n

=

30)

and

(c)

innon-pregnantcontrols(n =

27).

Valuesare mean±s.e.m.

The combined evidencesuggeststhat the

menstruating

intervalisassociated withareduction

of

_fecundity

which,

however,

is less

_complete

than it is

_during

the

_phase

of lactational amenorrhoea.

Effect of

suckling

upon

fertility

It is

_important

to understand the effect which different

suckling

patterns have upon the restoration of

_fertility

so that

appropriate

advice canbe

given

to

nursing

mothers who wishto

prolong

the interbirth interval for as

long

as

possible.

It is well known that the

phase

of

lactational amenorrhoea is much shorter

_during

_partial

as

compared

with full

(unsupplemented)

breast

_{feeding (Sharman,}

1951;

McKeown &

Gibson,

1954;

Perez et

_al,

_1972;

Chen et

_al,

1974).

Gioiosa

_{(1955) reported}

that,

out of 500 birth intervals in mothers who breast

fed,

46

(9-2%)

conceived

_during

lactation but 40 of these

(87%)

conceived when the

_weaning

process was

taking

place.

Gioiosa

(1955)

concluded that the

fertility protection

associated with breast

feeding

lasted for9 monthsormore,

provided

thatno additional

supplementary

or

complemen¬

taryformulawasused.

It is

clear,

therefore,

that

suckling

is a

_major

_{variable in the control ofpost-partum}ovulation

but

_relatively

few studies have

_attempted

tomeasurethe

suckling

stimulus. Konner & Worthman

(1980)

have

reported

that the

prolonged

interbirth intervals ofupto4 years amongthe nomadic

!Kung

hunter

_gatherers

are associated with very

frequent suckling

bouts,

which last for

only

2

min every 15 min. This suggeststhat very

frequent suckling

exerts a

profound inhibitory

_effect upon

_{reproduction.}

In

_Rwanda,

ruralwomenbreast feed ondemand and 50% conceive

again

within 23 months

after

_delivery;

_by

contrast, in urban women, breast

feeding

is

operated

on a more

rigid

schedule

with fewer

_{feeding episodes}

and 50% of mothers have conceived

_again

within 9 monthspost partum

(Bonte, Akingeneye,

Gashakamba,

Nbarutso &

_Nolens,

_1974).

In a series of

cross-sectional

studies,

Delvoye,

Badawi,

Demaeged

&

Robyn (1978)

found that

_prolactin

levels were related both tothe duration oflactational amenorrhoea and tothe

_frequency

of

suckling.

By

extrapolation,

these data suggest that the duration of lactational amenorrhoea is related to

the _pattern of

suckling

frequency.

These various studies

_point

to the

_profound

effect which

different

suckling

patternsexertuponpost-partum

_fertility.

Infantfeeding

patternsand thetime

_offirst

ovulation.Fromour own

_prospective

_studies,

_the

infant

_feeding

_patterns were

compared

between mothers who ovulated before 30 weeks_post

partum,those who ovulated between 30 and 40 weeks postpartumandthose who ovulated after 40 weekspost partum. The mothers who

postponed

ovulation for

longest (>40 weeks)

had a

longer

total duration of breast

_feeding

than did those in the other two groups, but there were

otherdifferences between the_groupsas illustrated in

Text-fig.

8;

the mothers who ovulated after

40 weeks maintained

suckling

duration and

frequency

at the

_highest

levels,

introduced

supplementary

food most

_slowly

and maintained

night

feeds for

longest.

The maintenance of

night

feeds

_(defined

as a

suckling episode

between

midnight

and 08:00

h)

_may be

important

because a

long

interval without

suckling

could allow the

hypothalamic-pituitary-ovarian

axis

sufficient timetorecover andresumeovulation. This

study suggested strongly

that therewas an

inverse

_relationship

between the use _of

supplementary

_{foods and} the

strength

of_the

suckling

stimulus,

and that the

_early

and

_abrupt

introduction of

supplements

might play

an

important

partin relationtothe

_resumption

ofpost-partumovarian

_activity

and ovulation. •>_{40 weeks}

O30-40 weeks

<_{30 weeks}

Weeks_{post partum}

Text-fig.

8.

_Comparison

of infant

_feeding

in mothers

_ovulating

before 30 weeks

_(N

=

7),

between 30 and 40(N=9)andafter40 weeks(N=9)postpartum.Values_{are mean}+_s.e.m.

Effect of supplementary food

on

suckling

and ovulation. The critical

importance

of

supplementary

food was

emphasized

by

centring

the levels of

suckling frequency

and

suckling

duration round the time at which

_supplements

wereintroduced

(Text-fig.

9). Suckling

duration

and

_{suckling frequency}

for the whole cohort of

breast-feeding

mothers remained

relatively

constant until

_supplements

were

given,

after which bothfell

abruptly.

These

changes

in

suckling

werereflected in thebasal

prolactin

concentrations

and,

beforetheintroductionof

supplements,

no mother had ovulated

although

four had evidence of ovarian follicular

development.

After

supplements, progressively

more mothers had evidence of ovarian follicular

development

and

52% had ovulated within 16 weeksof

_introducing

_{supplementary}

food.

Text-fig.

9. Mean

_suckling

duration,

suckling

frequency,

basal

_prolactin

andovarian

_activity

in

women

(N

=

27)

before and after the introduction of

supplementary

food. Values _{are mean}

±s.e.m.Broken line indicates upper limitfor_non-pregnantwomen.(FromHowieetal,1981.)

In

_Text-fig.

_10,

the

_feeding

patternsin the 52% who ovulated within 16 weeks of

_introducing

supplements

are

compared

with the 48% who continued to suppress ovulation over that time.

The mothers who ovulated reduced

_suckling

more

rapidly

and weaned more

abruptly.

The

stronger

suckling

stimulus amongst those who continued tosuppress ovulationwasreflected in

higher

meanbasal

prolactin

levels which remained above thenon-pregnantrange.

Sequence

ofevents

_leading

topost-partumovulation

From the data

_presented

in this paper, it is

possible

to formulate a

hypothesis

of the events

leading

to the return of post-partum ovulation. In

_{bottle-feeding}

_mothers,

_{plasma prolactin}

concentrationsreturntonormal within a few weeks of

delivery

and there isan

early resumption

of ovarian

_activity

and ovulation. In

_{breast-feeding}

_mothers,

_prolactin

values are elevated and

ovarian function is

suppressed,

theextentofthat

_suppression

_{being dependent}

_uponthe

strength

and duration of

_suckling;

the

suckling

stimulus is undermined

_by

theuse of

supplementary

food

which

_indirectly

encouragesthe

_resumption

ofovarian

_activity.

Intheir detailed

_study,

Perez et

100 -Supplementary food I +12 +16 10 +14

Text-fig.10.

_Comparison

ofinfant

_feeding

patterns and basal

_prolactin

between

_(o)

mothers

ovulating

within 16 weeks

_(N

=

14)

and

( )

mothers

suppressing

ovulation ( =

13)

after

introduction of

_{supplementary}

food. Values are mean +s.e.m. The broken line indicates the

upperlimit fornon-pregnantwomen.* <0-01. (FromHowieetal, 1981.)

Table 1.Percentage of

_{breast-feeding}

mothersgiving

_supplements

(occasionalor

regular)

in

economically

advantaged, urban poor and rural groups of different countries (from W.H.O. Collaborative Study on

Breast

_{Feeding, 1979)}

Country Group

2-3 months

6-7

months _{Country Group}

2-3 months All 46-8 96 Chile All 30-7 100 Advantaged Poor Rural 60 59 59 Advantaged Poor Rural 67-8 49-2 49-3 Guatemala 38-6 85-3 Advantaged Poor Rural 93 51 13 Advantaged Poor Rural 86-1 63-5 35-0 100 91 86 Philippines Advantaged Poor Rural 84 36 41 Advantaged Poor Rural 38-3 36-0 49-0 84 95 76 India Advantaged Poor Rural 52 5 1

ovulation or pregnancy but

they

did not define the

_{suckling frequency}

which constituted full breast

feeding

in their

_population.

Nevertheless,

it is clear that the

early

and

regular

use of

supplementary

food will have a detrimental effect onthe

_{contraceptive}

effect of breast

_feeding

and itmustbea matterofconcernthat theW.H.O.Collaborative

Study

on_breast

_feeding

_found

such a

high

use of

supplementary

foods among mothers from

developing

countries within 2—3

months_postpartum

_{(Table 1).}

Otherfactors

_influencing

lactational

_infertility

It has been

_suggested

that malnutrition may have an

impact

on the duration of lactational

amenorrhoea,

independent

of breast

_feeding

itself

(Thomson, Hytten

&

_Black,

_{1975). Bongaarts}

(1980)

has reviewed the evidence and concluded that chronic malnutrition had a

relatively

minor effect on

_fertility;

_for

_example,

the_{median durations of amenorrhoea}in

low,

_{medium and}

high

nutritiongroupsfrom

Bangladesh

were

21-2,

20-4 and 20-2 months

respectively (Huffman,

Chowdhury, Chakbarty

&

_{Mosley, 1978).}

Extreme food

_deprivation

during

famine, however,

exertsa

large

buttemporaryreduction in

fertility

(Bongaarts, 1980).

Lunn, Prentice,

Austin & Whitehead

_{(1980) compared}

two groups of

breast-feeding

Gambian

mothers,

one

receiving

a calorie

supplement,

the other

receiving

no such

supplement.

The mothers

_receiving

the calorie

supplement

had lower

_prolactin

concentrations and menstruatedmore

quickly.

This evidence

suggested

that maternal nutrition

might

have aneffect on

fertility

but

interpretation

of data is made difficult

by

the

tendency

of

poorly

nourished

mothers to breast feed for

longer

and suckle more

frequently

than well nourished mothers

(Prema,

Naidu &

_Kumari,

_1979).

Future studieswhich

_investigate

the effects of nutritionupon

the

contraceptive

effectsofbreast

feeding

should have

_objective

measures both of

suckling

and

nutritionalstatus.

Age

has also been

_implicated

as a factor of

importance,

because the duration of lactational

amenorrhoea tendstobe

longer

in older than inyoungerwomen

(Jain,

Hsu,

Freedman&

Chang,

1970).

Practical

_implications

oflactational

_infertility

Reliability

of

breast

_feeding

as a

_{contraceptive}

_method. It _{has to be}

recognized

_{that breast}

feeding

cannot be relied upon as a _guarantee

against

_{pregnancy for} individual mothers. The

place

of breast

feeding

in

_fertility

control has to be considered in the context of all the other factors which are

pertinent

to a

particular population

andto each ofthe individuals within that

population.

The

_importance

ofbreast

_feeding

as amethod of birth

spacing

will

depend

_uponthe

availability

of alternative

_{contraceptive}

methods,

the

_willingness

of the mothers to use the

methods and the averageduration ofuseof any

particular

method.These factors vary

widely

in

different communities and breast

feeding

should be

_regarded

as a method of

_fertility

control

which should be

_exploited

_along

_with,

rather than instead

of,

alternative methods of

contraception.

Nevertheless,

breast

_feeding

continues tohavean

important

rolein birth

spacing

throughout

the

_world,

andenthusiastic

breast-feeding,

characterized

by frequent

and

_{energetic suckling,}

can

exert a

high degree

of

fertility protection, particularly

during

the

phase

of lactational

amenorrhoea.

Birth

_spacing

in

_developing

countries. The main

importance

of breast

feeding

as a

contraceptive

method is in

_developing

countries where alternative methods of

_family

_planning

are used

infrequently.

It is clear that the modern methods of infant

feeding,

withthe

early

and

frequent

useof

supplements,

willhave

profound

implications

on

fertility

_and

population

growth.

from the burdens of

_{childbearing,}

this must be matched

_by

increased

_availability

and use of

alternative

_{contraceptive}

methods. The abandonment of

prolonged

breast

_feeding,

without alternative

_{contraception,}

will shorten interbirth intervals and

_greatly

increase the burdens on

individual mothers and

_community

resources.

Breast-feeding practices

have

_implications

for infant

growth,

neonatal infection and birth

spacing.

Infant

feeding

_policies

should be

designed only

after

_recognizing

the

_importance

of all these

_competing

factors.

Strategies of

contraception.

Potter,

Masnick & Gendell

(1973)

have

_pointed

out

_that,

in

many

communities,

a

contraceptive

method may be used

only

for a _finite

_period

_{of time. If} a

contraceptive

method is

_{begun immediately}

after

_parturition,

there will bean

overlap

between the

time when the

_{contraceptive}

is used and the

_period

of

_post-partum

anovulation when

_protection

isnotneeded.

By

delaying

theintroduction of the

_{contraceptive}

_method,

theextentof the

_overlap

is

reduced,

and the

_{potential contraceptive efficiency}

increased. For

_example,

in

_Bangladesh,

Potter et al

₍₁₉₇₃₎

calculated that if the use of artificial

contraception

were

delayed

until 6

monthspost partum,

only

1 in200womenwould have conceived

by

that time. Morestudies are

required

in different communitiesto

_{develop strategies}

which

_exploit

post-partum

infertility

and

contraception

tothebest

_advantage.

Birth

_spacing

in

_developed

countries. In

_developed

countries the

_majority

of

breast-feeding

mothers will use a

contraceptive

method. Some of these

mothers, however,

dislike the

inconvenience and the

_potential

side-effects of the various methods and

regard

the

_possibility

of

using

the

_{birth-spacing}

effect of breast

_feeding

as an attractive alternative. These mothers will

haveto breast feed

_{enthusiastically}

and acceptthat the method is not

_absolutely

reliable. More

work is

_required

todefinetheminimum

_{suckling frequency}

and duration whichare_necessaryto

inhibit ovulation

_reliably

but a number of

guidelines

canbe

_{tentatively suggested}

tothose who wish to maximize the

_{contraceptive}

effect. Mothers should feed on demand and use

supplementary

bottles as

infrequently

as

possible.

When it becomes

nutritionally

necessary for solid foodtobe

given

tothe

_baby,

this should beintroduced

gradually

andnot

_abruptly.

Mothers should be

encouraged

tobreastfeedat

night

and avoid

long

intervals between

suckling.

These

_{guidelines lay}

the

_emphasis

on

suckling

and

require

much enthusiasm on the part of

the mother. Breast

_feeding

is a

complex

physiological

process with functions

_beyond

those of infant nutrition alone. It is

_important

that,

inthe

future,

the advice and supportwhichis offered

tomothers should be formulated with full realization of all the

_implications

which breast

_feeding

has for both maternal and child health.

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