First-trimester volumetry includes measurement of the volume of the placenta (PV), embryo (EV), fetus (FV), gestational sac and yolk sac. PV, EV/FV ratio and gestational sac volume are correlated ...

“Due to the increased risk of miscarriage during the first trimester, pregnant aircrew are restricted from flying up to the first 12 weeks of the gestational period,” the release specified.

One of the common causes of a miscarriage is an anembryonic pregnancy, or blighted ovum in which the gestational sac ... of approximately 50 percent of first trimester miscarriages, according ...