Klinisk institutt 2
Midway evaluation

Midway evaluation - Henriette Hellebust



Fetal growth: maternal influence and outcome at birth


While it has been shown that fetal growth is under the influence of maternal factors during the latter part of pregnancy, this study tests the hypotheses that fetal growth is influenced also during the first and second trimester. Secondly, it is hypothesized that low fetal growth velocity carries an increased risk for adverse outcome.


I. As part of the multicenter study “WHO multicenter study for the development of Growth Standards from fetal life to childhood: The fetal component” 140 healthy women were recruited in Bergen. During first trimester maternal height, weight, BMI, and body composition were assessed and their influence on fetal crown rump length and yolk sac diameter was determined before 13 weeks gestation. Fetal biometry was reiterated during pregnancy. Z-scores were used for the statistical analysis.

II. Data from the «Fetal age and growth» study that included 650 healthy pregnant women, were used to examine the effect of maternal weight gain on fetal abdominal circumference at gestational week 15-25. Z-scores were used in a linear regression analysis.

III. “Fetal growth and neonatal outcome” is a study in progress aiming at including 220 women with high risk pregnancy to conduct repeat fetal biometry and Doppler measurements. Unconditional centiles and conditional centiles for estimated fetal weight and growth velocity are calculated at each visit and delivery mode and neonatal outcomes are registered after birth.


I. Based on 120 successful yolk sac measurements a linear regression showed that maternal weight, height and lean body mass were inversely related to the yolk sac diameter (p = 0.021, p = 0.013 and p = 0.044). However, this effect was valid only for female fetuses. The yolk sac/CRL ratio was negatively related to the fetal abdominal circumference at 24 weeks gestation (p = 0.047), but not later in pregnancy. This effect was only valid for male fetuses (p = 0.042).

II. Based on the complete data of 515 women we found a positive association between maternal weight gain and fetal abdominal circumference in second trimester (p = 0.001), with the strongest effect in women with less weight gain (p < 0.001).

III. So far 219 of the 220 participants have been included in the study.The data will be analyzed once all neonatal outcomes are registered.  


Maternal body size, body composition and weight gain during pregnancy influences fetal development during the first and second trimester (I and II). The fact that the yolk sac was larger when mother’s body was small (I) supports the concept that the yolk sac size is grown larger to increase transportation of nutrients when resources are less. It is interesting that the effect applies particularly to maternal lean body mass with a differential effect on the fetal sexes. The effect of the yolk sac size can be traced at 24 weeks of gestation but not beyond when other regulatory mechanism are in operation (e.g. fetal liver). Maternal weight gain has a positive effect on fetal abdominal circumference in the second trimester (II). The fetal abdominal circumference reflects the size of the fetal liver.