Joan I. Schall

Fetal growth and the etiology of preterm delivery

Objective To confirm that preterm delivery is associated with fetal growth restriction (FGR), and to determine if the various etiologies of preterm delivery are associated with the same degree and type of FGR. Methods Two hundred ninety young, primarily minority gravidas who had routine initial ultrasound examinations also had subsequent ultrasound examinations at 32 weeks gestation. Fetal growth characteristics were compared between preterm (less than 37 weeks gestation) and term deliveries, and among preterm deliveries with medical or obstetric indications, premature rupture of membranes (PROM), and spontaneous preterm labor. Results Forty-six infants (15.9%) were born preterm. At 32 weeks gestation, all fetuses later delivered preterm were already smaller than fetuses later delivered at term (P < .05) for all dimensions: head circumference (HC), abdominal circumference (AC), biparietal diameter (BPD), and femur length (FL). However, after stratifying by cause of preterm delivery for those fetuses later delivered for medical or obstetric indications, we found that only AC was decreased (P < .01) and that the HC-AC ratio was elevated (asymmetric FGR). Neonates delivered after unsuccessfully treated PROM or preterm labor were symmetrically smaller in all characteristics (HC, AC, BPD, and FL). Conclusion By 32 weeks gestation, fetuses later delivered preterm are already significantly smaller than fetuses later delivered at term. However, when stratified by the etiology of preterm delivery, infants delivered preterm for medical or obstetric indications had asymmetric growth patterns, which suggests a growth failure late in pregnancy. Infants delivered preterm after PROM or after failed or no tocolysis for spontaneous preterm labor were proportionately smaller, implying an overall slowing of growth that may originate early in pregnancy and possibly demonstrate a more chronic stress.

YOUNG MATERNAL AGE AND PRETERM LABOR

PURPOSEnThe relationship among young age, biologic immaturity (as indexed by low gynecologic age), and the causes of preterm delivery (idiopathic preterm labor [PTL], premature rupture of the membranes [PROM], and medical indications) were investigated among 605 primigravidas from the Camden Study.nnnMETHODSnThe sample consisted of 366 young adolescents < 16 years at the time of their last menstrual period (LMP) and 239 older women, 18-29 years at LMP (controls). The young adolescents were significantly shorter, thinner, had younger ages at menarche, and over a third (36.3%) were of low gynecologic age, i.e., their chronologic age was 2 or fewer years more than their age at menarche.nnnRESULTSnAdjusting for ethnicity, cigarettes smoked/day, weight gain rate, height, fetal sex, gestational diabetes mellitus, and pregnancy-induced hypertension, young adolescents overall had a nearly 75% increased risk of PTL (adjusted odds ratio [AOR] = 1.74, 95% confidence interval [95% CI]: 1.07-2.84), and preterm delivery with PTL (AOR = 2.08, 95% CI: 1.08-4.00). There was a modest decreased risk of preterm delivery among young gravidas attributable to other causes, such as PROM or medical indications (AOR = 0.70, 95% CI: 0.28-1.75). This increased risk of PTL and preterm delivery with PTL was principally attributable to biologic immaturity. Young age with low gynecologic age was associated with a twofold risk of PTL (AOR = 2.15, 95% CI: 1.19-3.89) and preterm delivery with PTL (AOR = 2.64, 95% CI: 1.23-5.65), while the risk associated with young age and higher gynecologic age was only increased moderately.nnnCONCLUSIONSnYoung adolescents, and especially those of low gynecologic age, appear prone to PTL and are at increased risk for preterm delivery through this pathway.

Maternal Growth and Fetal Growth: Pregnancy Course and Outcome in the Camden Study

The Camden (New Jersey) Study of maternal growth during adolescent pregnancy has demonstrated that even when adolescents have larger pregnancy weight gains than mature women they bear infants of the same or smaller size. Moreover growing adolescents were found to produce infants who weighed an average of 127 g less at birth than infants of already grown adolescents. Also recorded in growing adolescents were significantly lower third-trimester serum concentrations of the nutrients ferritin and folate. Adolescent gravidas growing as indicated by the Knee Height Measurement Device had more than a two-fold increased risk of a high systolic/diastolic (S/D) ratio suggesting that maternal growth influences the vascular resistance of the placenta from the fetal side. A high S/D ratio is associated with impaired blood flow and diminished fetal growth. Overall evidence from the Camden Study suggests a competition between the still-growing mother and her fetus that is present even when the adolescents diet is comparable to that of a pregnant adult the weight gain is sufficient and maternal energy stores as fat are abundant. In this competition the metabolic needs of the mother take precedence over the needs of the fetus. Unlike risk factors associated with maternal social class maternal growth has the potential to occur more frequently among more affluent adolescents.

Implications of the Camden Study of Adolescent Pregnancy: Interactions Among Maternal Growth, Nutritional Status, and Body Composition

One of the principal goals of the Camden Study over the past decade has been to document the extent to which pregnancy during adolescence is affected by continued maternal growth. Findings from the Camden Study relating to the other main goal, the effects of maternal growth during pregnancy on the outcome of pregnancy (maternal-fetal competition), are reviewed elsewhere. Contrary to widely held beliefs, we have found that there is considerable growth in late adolescence for girls, and, in particular, continued development of weight (> 1 kg/year) and increases in subcutaneous fatness at central sites. Thus, when pregnancy occurs during this final phase of adolescent growth, the normal growth processes may be exacerbated. That is, the adolescent potential for weight gain (as fat) may be exploited. Along with others, we have documented that adolescent pregnancy is associated with larger gestational weight gains. Using methods sufficiently sensitive to detect maternal growth prospectively, we also found that the larger-than-average total weight gains among adolescents appear attributable primarily to the growing adolescent gravidas and reflect their continued accrual of subcutaneous fat and increased risk for weight retention. Excessive gestational weight gain, as is more common among growing adolescent gravidas, appears to exacerbate the accumulation of fat at central sites. Aside from the consequences to the outcome of pregnancy, adolescents who begin their childbearing early while still growing themselves, such as those we have followed in the Camden Study over the past decade, may be at particularly increased risk for overweight and obesity. Further, the excessive deposition of subcutaneous fat at central body sites, as we have documented for adolescent pregnancy, will often in later life presage the development of cardiovascular disease, noninsulin-dependent diabetes mellitus (NIDDM), and hypertension. Thus, far from being benign, pregnancy during adolescence, particularly when the adolescent is herself still growing, may contribute to long-term risk for obesity-related diseases and diminish the quality of life.

Maternal Growth during Pregnancy and Lactation

Until recently, it was widely accepted that the small amount of statural growth observed in young gravidas was unlikely to be clinically significant, to alter maternal nutritional status, or to threaten fetal growth. We show that this belief reflects incomplete information about growth and the use of inappropriate measuring techniques by investigators. We have done this using illustrations drawn primarily from the Camden Study, a controlled, prospective study of nutrition and growth during adolescent pregnancy. Maternal growth during pregnancy is prevalent and associated with increased gestational weight gain. In the postpartum period it is associated with increased triceps skinfolds, arm fat area and weight retention, all of which occur at caloric intakes comparable with those of pregnant, non-growing adolescents and mature women. Unlike pregnancy where research is continuing, the sequelae of maternal growth during lactation are virtually unstudied.

Sex differences in the response of blood pressure to modernization

Sex and age differences in the incidence of hypertension and blood pressure (BP) levels and their concomitants are examined among the Manus of Papua New Guinea in the context of modernization. For Manus men, BP increases directly with both degree of modernization and duration of migration to the local towns and larger cities of Papua New Guinea, accompanied by similar increases in body mass and subcutaneous fat. For Manus women, however, although body mass and fatness increase along the modernization continuum, BP does not. Risk for hypertension (140/90 mm Hg) was increased fourfold among men who resided in town (adjusted odds ratio [AOR] = 4.4, 95% confidence interval [CI] 1.5–13.2) and also among those who were in the highest tertile of fatness (AOR = 4.1, 95% CI 1.6–10.4). Among women, older age (≥45) alone significantly increased risk tenfold (AOR = 10.5, 95% CI 1.7–66.8). Using a Mantel‐Haenszel χ2, a meta‐analysis of sex and age differences in relative risk for hypertension (160/95 mm Hg) among 20 Pacific populations, 9 traditional living and 11 undergoing modernization, was performed. While young men showed increased risk in modernizing populations (summary relative risk [SRR] = 1.34, 95% CI 1.12–1.60), older men had significantly reduced risk for hypertension compared with women in both traditional (SRR = 0.46, 95% CI 0.33–0.64) and modernizing groups (SRR = 0.70, 95% CI 0.59–0.84). This crossover between the sexes with advancing age is also evident for BP levels in a larger sample of societies and suggests a biological basis for hypertension risk.

Excessive gestational weight gain and chronic disease risk

Excessive deposition of central body and abdominal (centripetal) fat early in life often will presage the later development of cardiovascular and metabolic diseases. Data from urban, low‐income women from Camden, New Jersey, were used to examine the influence of gestational weight gain on patterns of weight change and fat deposition in 118 young women followed over two consecutive pregnancies. Adjusting for confounding factors, there was a significant (P < 0.05) dose‐response relationship between the amount of gestational gain (in the subsequent pregnancy) and increases in postpartum weight compared with the postpartum in the prior pregnancy: +1.5 kg with a low gain, +2.9 kg with recommended amounts of gain, and +7.9 kg with excessive gain. Excessive gain (18+ kg) was common (18%) in the sample. The incidence of “new” obesity (body mass index [BMI] >29.0 in the subsequent postpartum but not the index postpartum) increased significantly with gestational gain: 4.7% with low gain, 7.0% with recommended gains, and 25.0% with excessive gain. There were similar dose‐response increases related to gestational weight gain in all skinfolds (suprailiac, subscapular, and triceps) and the sum of the skinfolds. However, in women with excessive gains, fat was increased disproportionately at upper (+52%) and lower (+48%) central body sites, compared with the periphery (+27%), and compared with increases in women with lesser gestational gains. Thus, excessive gestational weight gain, which is common among low‐income women, may be a factor which promotes obesity and a centripetal fat pattern during the reproductive years, thereby increasing the risk for cardiovascular and metabolic diseases in later life.

Growth of postmenarcheal girls from three ethnic groups

Documentation of normal growth in late adolescence has been limited to a few studies using largely white participants. Annual growth rates of 668 high school girls who had already achieved menarche were determined for stature, sitting height, and knee height measured using the Knee Height Measuring Device (KHMD), an instrument with superior reliability. The sample was 61.4% white, 16.8% Puerto Rican, 15.7% African American, and 6.1% girls of other ethnic backgrounds. Median growth rate was 1.5 cm/year for stature, 1.1 cm/year for sitting height, and 2.7 mm/year for knee height in the first full year after menarche, and >80% of all girls grew in at least one dimension. Growth in stature (≥1 cm) continued for 64% of girls 1 full year after menarche and for 31% of girls 2 years after menarche, and growth in knee height (≥1 mm) continued in >45% of girls up to 5 completed years past menarche. Whites, African Americans, and Puerto Ricans showed small but significant differences in amounts of postmenarcheal growth in the dimensions measured. African‐American girls grew less in stature and sitting height than other groups, whereas Puerto Rican girls grew significantly more in sitting height and significantly less in knee height than other ethnic groups. These findings demonstrate that, as documented in other studies of postmenarcheal growth, there is substantial growth after menarche in most girls. The most sensitive measures indicate that small amounts of growth persist >5 years after menarche. Appreciation of this phenomenon needs to be communicated to clinicians who generally assume that growth ceases at/or just after menarche.