The growth of the human embryo. A longitudinal biometric assessment from 7 to 12 weeks of gestation

Longitudinal studies of multiple parameters in the first trimester for assessment of embryonic growth are lacking. This study's aim was to register changes in growth over time, by taking several measurements of embryos on successive occasions and evaluating these changes by longitudinal analysis.This prospective longitudinal study describes the normal embryonic growth in vivo. Inclusion criteria were non-smoking women with single uneventful pregnancies, regular menstrual periods (28-30 days) and no hormone therapy in the 3 months prior to the pregnancy. Exclusion criteria were pregnancy complications such as diabetes, pre-eclampsia, delivery of preterm or growth-restricted infants. Of 36 recruited pregnant women, 29 met these criteria. Each pregnancy was examined five times between 7 and 12 weeks of gestation. This resulted in a two-level data set, where level 1 consisted of the observations and level 2 consisted of the individuals. The longitudinal data were analyzed with a software package specially created for multilevel analysis.The growth of the biparietal diameter (BPD), occipitofrontal diameter (OFD), mean abdominal diameter (MAD), chorionic cavity diameter and amniotic cavity diameter was constant; the growth of the crown-rump length (CRL) and the yolk sac diameter was not constant. Variation in the data sets was mainly caused by variation between the embryos/fetuses.The measured parameters except for the yolk sac showed a high degree of uniformity with virtually the same growth velocities. The yolk sac demonstrated uniform growth until week 10 only. Differences between the gestational age based on the last menstrual period and the true gestational age, and/or differences in the early growth of the embryos before the start of the study at 7 weeks, may have contributed to the variation between the individuals.