• No results found

ANTEPARTUM CARE

Beneficial Interventions

Maternal Nutrition Alterations in fetal growth described in multiple gestations have been attributed, in part, to the intensified fetal competition for maternal nutrients.

This inherent competition results in a drain on maternal resources and an accelerated depletion of maternal reserves. Placental transfer of an adequate nutrient supply is diminished after a combined fetal weight of 3,000 g is exceeded. Unfortunately, most of the investigations that have evaluated the impact of nutrition on perinatal outcome have involved singleton gestations, overlooking the prenatal care of multiples. This is unfortunate because there is accumulating evidence that nutrition is an important and modifiable variable which can improve intrauterine fetal growth and potentially lengthen gestation. The constrained pattern of fetal growth experienced by multiples makes environmental factors, such as nutrition, a greater influence on ultimate fetal growth than in singleton gestations. This allows a proportionately greater opportunity to positively influence birth weight and pregnancy outcome in multiple gestations by modifying maternal nutrition and monitoring the rate of maternal weight gain. Studies have identified maternal weight gains of 24 lbs by 24 weeks and overall weight gains of 40 to 45 lbs as being associated with optimal pregnancy

outcomes defined as an average twin birth weight of 2,500 g. A 35- to 45-lb weight gain has been recommended in normal weight women with twins. Investigators have noted the importance of adequate early weight gain (<24 weeks gestation). A ripple effect of maternal weight gain on fetal growth has been demonstrated with gains before 20 weeks and between 20 to 28 weeks influencing subsequent twin growth from 20 to 28 weeks and 28 weeks to delivery, respectively. Poor weight gain prior to 24 weeks (<0.85 lbs per week), regardless of the rate of gain after 24 weeks, has been associated with both reduced intrauterine growth and higher perinatal morbidity.

Studies among large cohorts of multiples have demonstrated that maternal weight gain prior to 20 weeks and between 20 to 28 weeks had a greater effect on birth weight in both twin and triplet pregnancies than did weight gain in the third trimester. These findings were particularly notable among underweight women. Patterns of higher maternal weight gain throughout pregnancy results in a favorable combined twin birth-weight difference of more than 1 lb at term compared to low patterns of maternal weight gain. Almost certainly, weight gain recommendations for twins need to be modified based on the maternal body mass index just as they are for

singletons. Analyzing patterns of both intrauterine fetal growth and twin birth weights, Luke and colleagues have proposed BMI-specific weight gain guidelines for twin pregnancies. These guidelines were modeled using multiple regression analysis for the gestational periods of 0 to 20 weeks (early), 20 to 28 weeks (middle), and 28 weeks to delivery (late). As might be expected, excellent twin growth was achieved with lesser maternal weight gains among overweight and obese women compared to underweight or normal weight women. Optimal rates of fetal growth and optimal birth weights were associated with BMI-specific rates of maternal weight gain (lb per wk) as described in Table 14.2.

TABLE 14.2. Body mass index: specific weight gain recommendations for women pregnant with twins

In an analysis of over 1,000 triplet pregnancies, Elster and colleagues identified male gender, older maternal age, increased parity, maternal height, pregravid weight, and maternal weight gain as factors associated with improved intrauterine fetal growth. They noted that a longer length of gestation was associated with higher

maternal age, parity, and weight gain. Maternal weight gain was also associated with higher birth weight, improved birth weight for gestational age, and a longer length of gestation in a study of 144 triplets reported by Luke. Regression analyses again indicated that periods of maternal weight gain with the greatest impact on triplet birth weight were from conception to 20 weeks and between 20 and 28 weeks gestation. Maternal nutrient requirements are all increased in multiples. Due to the greater expansion of blood volume, increases in maternal tissues (body fat, muscle, breast, uterine) and fetal mass, caloric requirements are estimated to increase by about 40% in twins and by 80% in triplets. Although there are no national guidelines, an estimate of individual nutrient needs in multiples is provided in Table 14.3 based on the recommended daily allowances for nonpregnant and singleton pregnancies published by the National Research Council, Food and Nutrition Board, and

extrapolations for twin and triplet pregnancies published by Luke.

TABLE 14.3. Recommended dietary allowances (RDAs) for nonpregnant women and women pregnant with singletons and estimated dietary requirements for women with twins, triplets, and higher order multiples a

Maternal anemia, both the iron and folate deficiency types, are common in multiples. Many have recommended supplementation of the standard prenatal vitamin with iron (60 mg per day) and folic acid (1 mg per day) when a multiple pregnancy is diagnosed. The frequency of maternal anemia is related to the overall nutritional status of the woman, which reemphasizes the need for adequate nutrition with a focus on heme-rich protein intake and an emphasis on folate-containing green leafy

vegetables. Other nutrients often lacking in women's diets include calcium, magnesium, and zinc, and their specific supplementation has been recommended by some to both prevent their depletion and to reduce pregnancy complications. There is good evidence that intensive patient education, aggressive nutritional counseling, and an emphasis on early and appropriate maternal weight gain can all contribute to improved intrauterine growth and perinatal outcomes in multiple gestations.

Ultrasound Ultrasound plays numerous critical roles in the antepartum care of multiples. These include their diagnosis, determination of amnionicity and chorionicity, identification of fetal or placental anomalies, evaluation of fetal growth and amniotic fluid volume, evaluation of fetal biophysical parameters, and determination of presentation. Accurate determination of chorionicity and amnionicity is important in antepartum management. Monochorionic pregnancies are at substantially higher risk for intrauterine growth restriction, growth discordance, congenital anomalies, and intrauterine fetal death. Although rare, monoamniotic placentation represents an extreme risk with high rates of twin-to-twin transfusion, cord entanglement, and fetal demise. Dichorionic twins are at lower risk as this placentation does not carry the potential for vascular communication and is associated with a lower risk of congenital anomaly. The value of antepartum ultrasound for the identification of fetal

congenital malformations has already been described. If two separate placentas are identified or if the fetuses are of different sex, the placentation is dichorionic. A thin, wispy membrane along with a single placenta and same sex fetuses suggest monochorionicity. There are several membrane characteristics that can help

differentiate a monochorionic placenta from a fused dichorionic placenta. A “thick” dividing membrane composed of four layers suggests dichorionicity. Another helpful characteristic is the “twin peak” or “lambda sign”. The “twin peak” represents a wedge-shaped projection of placental tissue extending above the fused chorionic

surface and separating the diamniotic/dichorionic intertwin membrane. Using these criteria, chorionicity can be predicted accurately in more than 80% to 90% of twin gestations. Determination of chorionicity is most accurate in the first trimester; as pregnancy progresses, the dividing membrane progressively thins and the likelihood of placental fusion increases. Few studies have specifically addressed either the value of serial ultrasound assessment of fetal growth or the appropriate interval for screening. It can be easily inferred, however, that ultrasound has an important role. Intrauterine growth restriction is three times more common among twins compared to singletons and ultrasound is the only modality capable of assessing individual fetal growth. In twin gestations, asymmetric growth restriction becomes increasingly more common as gestational age advances. The presumption is that ultrasound will allow identification of multiples with growth restriction resulting in antenatal surveillance or delivery which may improve perinatal outcome. Evidence of improved outcomes in multiples through the use of ultrasound is limited. In the routine antenatal diagnostic imaging with ultrasound (RADIUS) trial, twins were diagnosed both more consistently and at earlier gestational ages than in the control group receiving selective ultrasound. More than a one third of the triplets in the control group were not diagnosed until after 26 weeks gestation and approximately 10% were not diagnosed until the onset of labor. The RADIUS trial demonstrated a 50% reduction in the incidence of composite adverse perinatal outcomes among the multiple gestations in the routinely screened group. While this reduction was dramatic, it was not statistically significant since the trial was not powered to identify differences in the multiple gestation subgroup. A 10-year study of routine ultrasonography in Europe involving over 22,000 women and 249 multiple gestations also revealed

improved perinatal outcomes associated with routine earlier detection by ultrasound. Ultrasound is critical to the management of both twin and triplet gestations. In the second half of gestation, fetal growth should be assessed periodically by serial ultrasound examinations. Most clinicians repeat these ultrasounds on a monthly basis although the appropriate interval between scans has not been determined. This interval can likely be extended if previous examinations suggest appropriate fetal growth, especially in dichorionic gestations.

Selective Multifetal Pregnancy Reduction Gestational age and birth weight at delivery are the two most important factors determining perinatal morbidity and mortality and both are inversely proportional to the number of fetuses present. According to the U.S. Vital Statistics, the average birth weight and gestational age for singletons is 3,358 g at 39.3 weeks, compared to 2,500 g at 36.2 weeks for twins and 1,698 g at 32.2 weeks for triplets. Data from smaller reviews suggest that the average birth weight and gestational age is about 1,455 g at 30.5 weeks for quadruplets and 980 g at 29 weeks for quintuplets. These higher order multiples are at significant risk of delivery prior to viability and for those who reach viability, an appreciable risk of serious long-term morbidity. Expectantly managed triplets and quadruplets have a 20% to 30% risk of delivery prior to 24 weeks and an 8% to 12% risk of delivery between 24 to 28 weeks. Multifetal pregnancy reduction has emerged as a procedure meant to improve the chances of survival and health in higher order multiple gestations. The overall pregnancy loss rate prior to 24 weeks gestation following multifetal pregnancy reduction has dropped from initially reported rates of 15% to 20% to approximately 5% to 8% as experience with the procedure has increased. The risks of pregnancy loss and early preterm birth following multifetal pregnancy reduction have also been described based on the accumulated

experience of a consortium of national and international centers. The loss rate prior to 24 weeks is related to both the starting and finishing number of fetuses. A higher starting number is associated with a greater pregnancy loss rate. The loss rate under 24 weeks gestation fell from 15.4% to 11.4%, 7.3%, 4.5%, and 6.2% with six or more, five, four, three, and two fetuses present, respectively, at the start of the procedure. The optimal finishing number of fetuses appears to be twins with loss rates at =24 weeks of 10.9%, compared with 13.7% and 18.0%, respectively, for singletons and triplets. The preferred technique is the transabdominal, ultrasound-guided, fetal intracardiac injection of potassium chloride. It was initially believed that women with quadruplets or more would be ideal candidates for multifetal pregnancy reduction. A meta-analysis of the effect of multifetal pregnancy reduction on pregnancy outcome demonstrated that reduction to twins is associated with longer gestations, higher birth weights, and lower NICU admission rates. The incidence of maternal antenatal hospitalization, preterm labor, and cesarean birth are also reduced although incidences of preeclampsia, gestational diabetes, and other pregnancy complications are not. Somewhat more controversial has been the value of multifetal pregnancy reduction in triplets. Smaller series have not identified an improvement in perinatal mortality in reduced versus nonreduced triplets. Several investigators have reported a significant reduction in early preterm births (24–32 weeks) among triplets reduced to twins compared to nonreduced triplets. Because early preterm birth is a known risk factor for disability, reduction of triplets to twins may reduce the rate of serious morbidity and improve the quality of life for those remaining. Two relatively large databases that have specifically addressed the issue of reduction of triplets to twins have identified better outcomes for the reduced triplets including decreased fetal loss prior to 24 weeks, decreased severe prematurity, increased gestational age at delivery, increased birth weights, decreased perinatal mortality, decreased neonatal respiratory morbidity, and decreased interventricular hemorrhage. It is also important to be aware of the psychological

implications for mothers undergoing multifetal pregnancy reduction. Follow-up studies of the emotional responses of women undergoing this procedure revealed that 70% mourned for the reduced fetus(es), but most of the depressive symptoms were mild and lasted only 1 month. For a few however, moderately severe sadness and guilt continued for a longer period. Ultimately, over 90% of the women concluded they would make the same decision again. In addition to multifetal pregnancy

reduction, selective fetal termination can sometimes be offered in order to allow a pregnancy to continue following identification of a serious or life-threatening

malformation in one twin. The most common indications for selective fetal termination include dizygotic twins discordant for fetal chromosome abnormality, serious fetal structural malformation, or one twin affected by a single gene disorder. Multifetal pregnancy reduction of triplet and higher order multiple gestations is associated with longer gestations, higher birth weights, and lower rates of perinatal morbidity. Multifetal pregnancy reduction of quadruplets or quintuplets would also be associated with significant reductions in perinatal mortality. Multifetal pregnancy reduction should be included in the counseling of all women with triplets and higher order multiples.

Serial Digital Cervical Examination The value of antepartum digital cervical examination lies in its ability to provide ongoing risk assessment. One cervical score is

calculated as follows: cervical length (cm) minus cervical dilation at the internal os (cm). A cervix that is 2 cm long with a closed internal os gives a score at +2. A cervix that is 1 cm long, dilated 1 cm at the internal os gives a score of zero. A cervix that is 1 cm long with an internal os dilated 3 cm gives a score of -2. A cervical score =0 on any single examination predicted preterm labor within 14 days in 69% of those women. When only multiparous women were considered, the predictive value rose to 80%. Newman and Ellings performed weekly digital cervical examinations on 86 twin and 7 triplet gestations as part of routine antepartum surveillance. There was a progressive fall in cervical score throughout the latter half of gestation, most notable after 30 weeks gestation. A cervical score =0 on or before 34 weeks gestation had a positive predictive value of 75% and a four-fold increase relative risk of delivery =37 weeks. The earlier in gestation that a cervical score =0 is detected, the greater the positive predictive value ascribed to it. Only two (2.6%) women experienced spontaneous preterm labor or PPROM within 1 week of having a cervical score greater than 0. A cervical score =0 is a marker of abnormal cervical status and increased preterm delivery risk. Conversely, women who maintain a cervical score greater than 0 are good candidates for continued observation without obstetric intervention. Ideally, these examinations should be done by a consistent examiner on an every 1- to 2-week basis between 24 to 36 weeks gestation. There are no prospective studies or cohort series that demonstrate that antepartum digital cervical examination is associated with obstetric complications or adverse perinatal outcomes.

Corticosteroid Administration Corticosteroids should be administered to women with multiples experiencing preterm labor prior to 34 weeks gestation. The National Institutes of Health also recommends corticosteroid therapy for women with PPROM at less than 30 to 32 weeks gestation. Corticosteroids have been shown to induce fetal lung maturity and reduce perinatal complications in twin gestations as well as singletons. Evaluation of the clinical characteristics and outcomes of twin gestations complicated by PPROM reveals that the nonpresenting twin was more likely to develop hyaline membrane disease, respiratory complications, and require more oxygen therapy than the presenting infant. As a consequence, the nonpresenting twin was at greater risk for infant mortality.

Fetal Surveillance Although no prospective trials exist, all retrospective reviews indicate that the nonstress test has equivalent efficacy in multiples to that seen in singletons. Both the nonstress test and the biophysical profile have been shown to be effective in identifying the growth-retarded multiple, the multiple at risk for

hypoxic/asphyxic injury, and the multiple at risk for perinatal mortality. One retrospective cohort study compared 230 twins who received third trimester nonstress tests to 435 twins who did not. Although the differences did not achieve statistical significance, there was only a single intrauterine fetal demise in the nonstress test group compared to nine in the control group. Similar findings have been reported in smaller retrospective studies involving triplet and higher order gestations. While the routine use of antepartum fetal surveillance in uncomplicated multiples has not been shown to be of benefit, surveillance is certainly indicated in those gestations identified as being at higher risk. These would include those with intrauterine growth restriction, abnormal fluid volumes, growth discordance, pregnancy induced hypertension, fetal anomalies, monoamnionicity, or any other pregnancy complications placing one or more of the fetuses at increased risk. Other recommended methods of fetal surveillance include fetal kick counting, although some patients may find it difficult to distinguish the movements of one fetus from those of another.

Umbilical cord Doppler velocimetry may be of help in evaluating growth-retarded fetuses. Ultrasonography obviously contributes to both the risk assessment and surveillance of multiple gestations. The limitations of ultrasound for both the diagnosis of intrauterine fetal growth restriction as well as for fetal growth discordance would be the major indication for some clinicians to recommend routine surveillance of all multiples. At present, antepartum fetal surveillance in multiples is

recommended in all situations for which one would perform similar surveillance in a singleton pregnancy. Further studies are needed to determine if routine antepartum fetal surveillance provides objective benefit in either twin or triplet gestations.

Controversial Interventions

Reduced Activities/Rest Activity restriction and increased rest at home is commonly recommended for women with multiples although there are no prospective randomized data evaluating this intervention. Existing data are both dated and limited by study design. Studies evaluating the role of prescribed rest in both twin and triplet gestations compared to similar pluralities with unrestricted activities typically date from time periods when the unrestricted multiples were in reality undiagnosed.

Maternal rest has been associated with reduced baseline uterine contraction frequency, and restricted activity has been generally accepted as a reasonable approach to the prolongation of pregnancy. Other studies have suggested that the birth weights of both twins or triplets may be increased if reduced activity and home bed rest is introduced in the mid-trimester. Further research is needed to define the impact of restricted activity and rest on both the duration of pregnancy, fetal growth, and the risk of pregnancy-induced hypertension.

Home Uterine Activity Monitoring Few issues are as controversial as home uterine activity monitoring (HUAM). HUAM has been advocated for multiples due to their increased risk of premature labor combined with observations that multiples may be less accurate in the self-detection of their own prelabor uterine activity compared to women with singleton gestations. Prospective randomized trials evaluating the efficacy of HUAM in multiples have provided conflicting results. Dyson and colleagues

Home Uterine Activity Monitoring Few issues are as controversial as home uterine activity monitoring (HUAM). HUAM has been advocated for multiples due to their increased risk of premature labor combined with observations that multiples may be less accurate in the self-detection of their own prelabor uterine activity compared to women with singleton gestations. Prospective randomized trials evaluating the efficacy of HUAM in multiples have provided conflicting results. Dyson and colleagues