A recent paper has been published in the international journal Ultrasound in Obstetrics and Gynecology. The authors concluded that early implantation leads to a larger CRL and late implantation to a smaller CRL at 10–14 weeks, independent of CRL growth rate. The conclusion is that Implantation timing is a major determinant of fetal size at 10 – 14 weeks and largely explains the variation in estimates of GA in the first trimester derived from embryonic or fetal CRL. The major finding of the study was that fetal size at 10 – 14 weeks’ gestation is mainly a composite of ovulation and implantation timing. This may prove to be a fundamental biological insight. Previously variations in size of the first trimester embryo were though to reflect the time from conception. This new study shows that the ovulation to implantation interval is a significant contributor. This work ties in with publications from Professor Jan Brosens group in Warwick. Brosens takes the view that defects in decidualisation leading to an abnormal implantation interval is a precursor to recurrent miscarriage. What is clear is that these events in early pregnancy are of real interest and will become the focus of research efforts in the next few years.
