Neonatal Outcome: Is Adolescent Pregnancy a Risk Factor?

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Neonatal

Outcome:

Is Adolescent

Pregnancy

a

Risk Factor?

Barry

Zuckerman,

MD, Joel

J. Alpert,

MD, Elizabeth Dooling, MD,

Ralph Hingson, ScD, Herbert Kayne, PhD,

Suzette

Morelock,

MEd

and Edgar Oppenheimer, MD

From the Boston University School of Medicine and School of Public Health, and Departments of Pediatrics, Socio-Medical Sciences, and Community Medicine, Boston City Hospital, Boston

ABSTRACT. It has been widely reported that adolescent

mothers are more likely to experience poor pregnancy outcome, especially low-birth-weight and/or premature infants. Recent data suggest that this poor outcome may

be attributed to confounding health and social

character-istics of adolescent mothers. A study of maternal health

and neonatal development at Boston City Hospital pro-vided an opportunity to assess whether adolescent

moth-ers deliver infants with poorer outcomes at birth than nonadolescents independent of numerous social and

health differences between adolescent and nonadolescent

mothers. A total of275 infants ofprimiparous adolescents

(aged 13 to 18 years) were compared at birth with 423

infants of primiparous nonadolescents. Size at birth,

length of gestation, Apgar scores, and birth trauma were

examined. The only statistically significant difference

between the two groups was that adolescent mothers

delivered infants whose mean weight was 94 g less (P <

.03) than infants of nonadolescent mothers. Multiple and

logistic regression analyses demonstrated that several

health and social factors, but not adolescent status, were independently associated with the measures of adverse

infant outcome. A subsequent regression analysis dem-onstrated similarly that being a younger adolescent (16 years and younger) did not independently predict low

birth weight at delivery or other measured adverse neo-natal outcomes. These data support the view that health and social factors are more important to poor fetal out-come among primiparous mothers than adolescent status. Some of the health factors are amenable to clinical inter-vention. Pediatrics 1983;71:489-493; adolescent preg-nancy, low birth weight, neonatal outcome.

The birth rate for girls less than 15 years of age and for all unmarried teenagers has risen while the

Received for publication March 22, 1982; accepted July 28, 1982.

Reprint requests to (B.Z.) Department of Pediatrics, Boston City Hospital, 818 Harrison Aye, Boston, MA 02118.

American Academy of Pediatrics.

overall birth rate in the United States has declined

in the last 10 years.1 If the present rate were to

continue, of all girls who are now 14 years old, 20%

will give birth during their teenage years.

Most reports of adolescent pregnancies indicate an increased risk of developing various pregnancy

complications and poor neonatal outcome, espe-cially maternal toxemia and low birth weight.2 Many of these reports have been criticized for not analyzing other factors such as health habits and prenatal care that may have confounded the

out-come. Low prepregnancy weight,7 black race,8 ad-verse social conditions,8 and narcotic use9 have been

associated with premature or low-birth-weight in-fants and the pregnant adolescent.

Merritt et al’#{176}reported a significantly increased

incidence in low-birth-weight infants for mothers aged 14 years or younger, with a nonsignificant trend toward increased low-birth-weight infants

among mothers 19 years or younger when compared

with nonadolescent mothers. However, they also documented more cigarette smoking, alcohol and drug use, and gonorrhea in the adolescent mothers. When Miller and Merritt’1 excluded high-risk

mothers from their analysis they found no

differ-ences in rate of low-birth-weight or premature

in-fants between adolescent and nonadolescent

moth-ers. Baldwin and Cai&2 and Perkins et al’3 con-cluded that inadequate prenatal care contributed to poor pregnancy and neonatal outcome more than did young age. Another study’4 reported no

differ-ences between children of adolescent and older mothers in terms of prematurity and birth weight.

In contrast, in a 1979 statement on teenage preg-nancy, the Committee on Adolescence of the Amer-ican Academy of Pediatrics15 attributed a greater

(2)

to Public Law 95-626 on Adolescent Family Life16 concluded that findings did indicate a higher

mci-dence of low-birth-weight infants among unmarried adolescents, especially young adolescents.

In a recent review, Lawrence and Merritt17

sum-marized the state of our knowledge: “It is yet to be

determined whether biologic or social inadequacies best explain the apparent reproductive

disadvan-tage of the American teenager and the well-being of their babies.”

A

study of maternal health and fetal development at Boston City Hospital (BCH) provided an oppor-tunity to further explore whether: (1) infants born to adolescents exhibit poorer outcomes at birth than infants born to nonadolescents; and (2) if the outcomes are poorer, whether adolescent status or

other health habits or life situations are more pre-dictive of those outcomes.

METHODS

From February 1977 to October 1979 all mothers delivering an infant in the maternity service at BCH were eligible to participate in the study after informed consent was obtained. Birth weight and Apgar scores were recorded by delivery room staff

on all infants at delivery. Infants in the study

received a physical examination after delivery in-cluding detailed neurologic and morphologic assess-ment by one of four study pediatricians. Seventy-five percent of the examinations took place within

the first three days after delivery. Measurement of length and head circumference were made on each

infant. Length was obtained by a measuring device

using a standardized technique. Dubowitz scores

were calculated on each infant to assess length of

gestation. Infant outcomes were also dichotomized

to indicate whether or not infants exhibited

char-acteristics of clinical risks: length of gestation less

than 37 weeks; five-minute Apgar score of less than 7; or infants with birth weight, length, or head circumference below the tenth percentile for

ges-tational age in the BCH sample. All examinations

were conducted without knowledge of the mother’s age or prenatal history. Following the examination, labor and delivery data were abstracted from the

infant’s record. Participating mothers were

inter-viewed by one of five English- or Spanish-speaking women. A 30- or 40-minute structured interview

focused on demographic information, health habits during pregnancy, present and past medical

prob-lems, attitudes, and support systems. A full

descrip-tion of the methodology and study sample has been

previously published.18

Among 1,962 mothers interviewed there were 315 primiparous adolescents (aged 13 to 18 years) and

498 primiparous nonadolescents (aged 19 to 30

years). Some days no study pediatrician was

avail-able to examine infants of either adolescent or nonadolescent mothers, and therefore not all of these interviewed mothers had their infants exam-med. In order to determine whether mothers whose

babies were examined differed from those whose

babies were not examined, the two groups were compared on a variety of characteristics. The

in-fants of 275/315 (87%) adolescent mothers were

examined. These mothers did not differ on 18

de-mographic and health habit variables from the 40 mothers whose babies were not. examined. Eighty-five percent (423/498) of the infants of the nona-dolescent mothers were examined. The only differ-ence between the 423 nonadolescent mothers whose babies were examined and the 75 mothers whose babies were not examined was that more mothers whose babies were not examined (70% v 57%; P <

.05) were black. The mother-infant pairs (423

non-adolescents and 275 adolescents) for whom

inter-view and examination data were collected are the

focus of this paper.

Univariate analyses were used to assess whether

the study sample of adolescent and nonadolescent mothers varied on numerous maternal

characteris-tics, labor and delivery events, and neonatal out-come measures. Stepwise multiple regressions

ex-amined which variables related to length of gesta-tion at birth, infant size at delivery, and Apgar

scores. The independent variables entered into the

multiple regression analyses were: drug use (never

Vprepregnancy or during pregnancy), prepregnancy

weight, number of previous pregnancies, religious affiliation (any/none), race (black/nonblack, His-panic/non-Hispanic), history of prior maternal

ill-nesses (eg, hypertension, diabetes), number of mis-carriages and abortions, risk factors (eg, toxemia,

epilepsy, anemia, accidents) during pregnancy, weight change during pregnancy, time of first pre-natal visit (first, second, or third trimester, or no prenatal care), daily coffee consumption, x-ray ex-posure during pregnancy (yes/no), number of ciga-rettes smoked per day during pregnancy, marijuana

use (never, prepregnancy, pre- and during

preg-nancy), education, number of meals per day, sex of infant, alcohol consumption (average daily drinks) prior to pregnancy and during pregnancy

sepa-rately, and iron use. Adolescent status included all women 18 years and younger.

In the analysis of the five-minute Apgar scores,

the following intrapartum risks were included as additional independent variables: whether the mother had premature rupture of the membranes, a cesarean section, meconium-stained fluid, oxyto-cm (Pitocin)-induced labor, medications during

la-bor, use and route of anesthesia, maternal fever,

(3)

or abnormal placenta, nuchal cord, decelerations,

intubation, and forceps extraction. Additional data

on infant status, including congenital

malforma-tions and weight at birth, were also added. A separate analysis was used to determine

whether being an adolescent in itself was independ-ently related to the infant clinical risk categories when other social, demographic, and habit pattern differences between adolescents and

nonadoles-cents were analytically controlled. As the clinical risk categories are dichotomous and not continuous

variables, multiple logistic regression analyses were used.

Because some researchers have reported that younger adolescents are the group at highest risk for adverse neonatal outcome, multivariate

anal-yses were repeated to examine whether adolescents

16 years and younger (N = 94) were more likely to

deliver infants with adverse outcomes.

RESULTS

Characteristics

of Mothers

Among adolescents in the study, 13% were aged

15 years or younger, 21% were aged 16 years, 31%

were aged 17 years, and 35% were 18 years of age.

The age distribution for the nonadolescents was

21% aged 19 years, 56% aged 22 to 25 years, and

22% aged 26 to 30 years.

A comparison

of the adolescent

and

nonadoles-cent mothers (Table 1) shows that pregnant

ado-lescents entered prenatal care later, were more

likely to have gonococcal infection during

preg-nancy, and had lower prepregnancy weight. The

adolescent mothers were more likely to be black, and they reported fewer religious affiliations. How-ever, unlike mothers in the study of Miller and Merritt’1 the primiparous adolescents were less

likely to engage in several behaviors that are thought to affect fetal growth adversely, such as cigarette smoking, alcohol consumption, and

psy-choactive drug use. The adolescent mothers also

were less likely to have roentgenograms taken dur-ing pregnancy.

Neonatal Outcome

Univariate analyses revealed no differences in

mean Apgar score at five minutes, mean birth length, mean head circumference, or presence of birth trauma (Table 2), between the infants of the two groups of mothers. Adolescent mothers deliv-ered infants whose mean birth weight was 94 g (P

< .03) less than infants of nonadolescent mothers.

TABLE 1. Demographic and Health Habits of Sample

Adolescents Nonadolescents P

N=275 N=423

% N % N

Race

Black 67.6 186 57.4 240 <.003

Hispanic 16.7 46 20.6 86

White 15.6 43 22.0 92

No religious affiliation 13.6 37 7.2 30 <.001

Prenatal visit, 1st trimester 59.7 160 74.3 306 <.003 Gonococcal infection during pregnancy 6.6 18 1.9 8 <.003 Roentgenograms during pregnancy 7.0 19 13.6 57 <.010 Cigarettes (2+ packs/day during preg- 9.2 25 16.2 68 <.001

nancy)

Psychoactive drug use during pregnancy 7.0 19 14.7 61 <.003 Alcohol cnsumption

2+drinks/dayprepregnancy 4.2 11 6.9 28 <.0004

2+ drinks/day during pregnancy 0.8 2 2.7 11 <.0005

Prepregnancy weight 100 lb 14.4 39 11.6 48 <.001

* Determined by x2 test of significance.

TABLE 2. Neonatal Outcome for Continuous Variables*

Adolescents (N = 275) Nonadolescents (N = 423)

Birth weight (g)t 3,102.11 ± 465.54 3,196.91 ± 519.48

Birth length (cm) 48.50 ± 2.46 48.83 ± 2.44

Head circumference (cm) 34.15 ± 1.49 34.32 ± 1.47

Apgar at 1 mm 7.57 ± 1.82 7.77 ± 1.63

Apgar at 5 mm 8.67 ± 1.21 8.82 ± 0.96

Gestational age (wk) 39.2 ± 1.44 39.33 ± 1.43

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* Determined by x2 test of significance.

t BCH, Boston City Hospital.

Infants born to adolescent and nonadolescent

mothers did not differ significantly in their propor-tions in any of the clinical high risk categories

(Table 3).

Because the adolescent and nonadolescent

moth-ers varied on many characteristics that might influ-ence infant outcome, multivariate analyses were undertaken to determine the independent

contri-bution of each variable and whether adolescent

status was independently associated with adverse

outcomes.

These analyses demonstrated that adolescent

status was not significantly related to the gesta-tional age at birth, or birth size of the infants of

these primiparous mothers. However, several other

variables had an independent effect on these out-comes. The regression analysis of birth weight is illustrative (Table 4). The $ coefficient describes the relative importance of each independent varia-ble in explaining variation in the infant outcomes. Mothers who gained less weight during pregnancy,

weighed less prior to pregnancy, were black,

deliv-ered male infants, and smoked marijuana during pregnancy delivered infants of lower birth weights.

Adolescent status was independently but weakly associated with lower Apgar scores at five minutes. Adolescents had five-minute Apgar scores that av-eraged .17 points lower than nonadolescents after controlling for length of gestation.

Logistic regression analyses were performed to

assess whether adolescent status was independently

associated with the high-risk clinical groupings de-scribed above. Again, adolescent status was not significantly associated with prematurity; presence of birth trauma; or infant birth weight, length, or

head circumference below the tenth percentile in each gestational age; nor was adolescent status

associated with five-minute Apgar scores of less than 7. This latter finding is in contrast to the

small difference in mean Apgar scores at five

mm-TABLE 3. Neonatal Outcome for Dichotomous

Varia-bles* Adole No. scents % Nona No. dolescents %

BCHt <10th percentile 27 10.0 44 10.5 birth weight

BCH <10th percentile 28 10.3 42 10.0

birth length

BCH <10th percentile 28 10.4 35 8.4 head circumference

Apgar at 1 mm <5 29 10.8 39 9.3

Apgar at 5 mm <7 24 9.0 27 6.5

Prematurity (<37 wk) 8 2.9 22 5.2

Birth trauma 7 2.6 14 3.3

TABLE 4. Multiple Regression Analysis on Birth

Weight*

Dependent Independent Variablest

Variable

Increase

in R2

fl-Coeffi-cient

Birth Gestational age

weight Weight change dur-ing pregnancy Weight prior to

preg-.28 .03 .03 .49 .18 .17 nancy Black/nonbiack Sex of infant Marijuana use .02 .01 .01 .10 -.10 -.08.

* N = 562; R = .63; R2 = .40.

t Variables significantly related to .05.

birth weight at P <

utes between the two groups. Most of the Apgar score differences between the two groups occurred at the upper, rather than the lower, end of the

Apgar score.

The replication of these analyses, which assessed whether younger adolescent mothers (aged 16 or

younger) experienced poorer fetal outcome, yielded results that were the same as for the older

adoles-cent group (18 years and younger). These younger adolescents did not experience a significantly higher rate of adverse outcome than older

adoles-cents or nonadolescents.

DISCUSSION

The pregnant primiparous adolescents from

BCH did not have the benefit of any special

inter-vention program. They did have access to prenatal

care, which they utilized, although they registered later than nonadolescents. Compared to nonadoles-cent mothers, adolescent mothers did not

demon-strate a greater incidence of infant risk factors such as prematurity, small size for gestational age, birth trauma, or five-minute Apgar score less than 7.

Similarly, no differences on other neonatal outcome

measures were demonstrated except that adolescent mothers had newborns whose mean birth weight

was 94 g less than older mothers. Hardy et al’9 reported a mean birth weight of infants of women 16 years or younger to be 130 g lower, compared to children of older mothers. However, in the present

study, when maternal characteristics and habits

during pregnancy were analytically controlled,

ad-olescent status, either 18 years and younger or 16 years and younger, was not associated with lower birth weight. This analysis did demonstrate a small but significant association of infants of adolescent

mothers having a lower mean Apgar score at five minutes.

The findings suggest that for the BCH

primipa-rous study population, adolescents are not at

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neonatal outcome. These results replicate findings

reported in other studies.’#{176}”4 The advantage of this

study is that data were collected prospectively and the analyses assessed the independent impact of

many factors that contribute to poor outcome.

However, there are limitations to the study that are important in interpreting the results.

First, the study population represents a

subsam-ple of a larger study that included women of all ages and parity. In the larger sample, increasing age,

measured as a continuous variable, was associated

with infants’ birth weight. In this study, adolescent status, defined either as women 18 years and

younger or 16 years and younger, was not associated

with infants’ birth weight. Second, this study did

not consider the increased neonatal risk posed by

repeat pregnancy during adolescence.2#{176} Third,

regression analysis could not be performed on the sample of adolescent mothers 15 years of age or

less, because of their small number. Therefore, the study does not rule out the possibility that this even

younger group of adolescent mothers is at an in-creased risk for poor neonatal outcome. Fourth, among the interviewed nonadolescent mothers, a higher proportion of black infants than infants of

other racial groups were not examined. Inasmuch

as the black mother is associated with the

low-birth-weight infant, this may have meant that the nonadolescents in our study had larger infants than the nonadolescent population at BCH. This sample bias increased the likelihood that we would find that adolescents have smaller babies.

IMPLICATIONS

The results of this study support the hypothesis

that for primiparous women, factors other than young age (16 years or less) are associated with low birth weight and other adverse neonatal outcomes.

The ability to demonstrate independent factors

that predict adverse neonatal outcome for pregnant adolescents provides a data base to develop specific intervention strategies to prevent these poor out-comes. Maternal health habits during pregnancy

such as low weight gain or marijuana use may be

amenable to clinical intervention. By appealing to the adolescent’s desire to maximize the health of her developing fetus, poor habits and behaviors may

be changed more easily during pregnancy than at

other times.

ACKNOWLEDGMENTS

This work was supported by grants R01-AA02446, R01-AA1257, and R01-AA02133-04 from the National

Institute on Alcohol Abuse and Alcoholism and grant

8427-6 from the William T. Grant Foundation.

We thank Michael Weitzman, MD, and Lorraine Kler-man, ScD, for their helpful suggestions and Jane Freeman

and Susan Simon for assistance in preparing the

manu-script.

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1983;71;489

Pediatrics

Suzette Morelock and Edgar Oppenheimer

Barry Zuckerman, Joel J. Alpert, Elizabeth Dooling, Ralph Hingson, Herbert Kayne,