Tracking of fetal growth characteristics during different trimesters and the risks of adverse birth outcomes

Abstract

Background: Fetal growth characteristics are used to identify influences of several maternal characteristics and to identify individuals at increased risk of adverse outcomes. The extent to which fetal growth characteristics track in different trimesters is not known.

Methods: In a population-based prospective cohort study among 8636 pregnant women, we examined the extent to which fetal growth characteristics track, are influenced by maternal socio-demographic and lifestyle related determinants and are associated with birth outcomes. Fetal growth was assessed in each trimester and at birth.

Results: Correlation coefficient between first-trimester crown-rump length and birthweight was r = 0.12 (P-value < 0.05). Correlation coefficients for fetal-head circumference, (femur) length and (estimated) fetal weight ranged from r = 0.16 to r = 0.30 (all P-values < 0.05) between second trimester and birth and from r = 0.36 to r = 0.58 (all P-values < 0.05) between third trimester and birth, and were highest for (estimated) fetal weight. Correlation coefficients for (estimated) fetal weight tended to be lower among overweight mothers, as compared with normal weight mothers, but were not influenced by other maternal characteristics. First, second and third-trimester fetal growth characteristics were associated with risks of preterm birth and small size for gestational age at birth,with the strongest associations present in third trimester.

Conclusion: Fetal growth characteristics track moderately throughout gestation, with stronger tracking coefficients present in later pregnancy. Tracking coefficients were not materially influenced by maternal socio-demographic and lifestyle characteristics. First, second and third trimester fetal growth characteristics were associated with the risk of adverse birth outcomes.

Keywords: Fetal growth; cohort study; preterm birth; small size for gestational age; tracking.

Figure 1.

Flow chart of the participants in the Generation R Study, 2001–05

Figure 2.

Longitudinal fetal growth patterns and the risks of adverse birth outcomes in the Generation R Study, 2001–05 (N = 8636)^{a a}Fetal growth among preterm born infants (A), fetal growth among post term born infants (B), fetal growth among small for-gestational-age infants (C), fetal growth among large for-gestational-age infants (D). Results are based on repeated measurement regression models and reflect the differences in gestational-age-adjusted SDS scores of fetal head circumference, length and weight growth for preterm born infants and post-term born infants compared with term-born infants in second trimester, third trimester and at birth and for small for-gestational-age infants and large for-gestational-age infants as compared with appropriate size for-gestational-age infants in second trimester, third trimester and at birth, respectively (reference group represented as zero line). Results for spontaneous preterm birth were similar (not shown). Head circumference, length and weight growth characteristics used in the models in the fetal period: second and third trimester, head circumference, femur length and estimated fetal weight; at birth, birth head circumference, birth length and birthweight. Model information is given in the Supplementary data available at IJE online.