The gestational sac GS is the earliest sonographic finding in pregnancy. It will be difficult to see if the mother has a retroverted uterus or fibroids. The GS is an echogenic ring surrounding an anechoic centre. An ectopic pregnancy will appear the same but it will not be within the endometrial cavity. Gestational sac size should be determined by measuring the mean of three diameters.
Also, in many countries, they check for Down syndrome at the dating scan. The sonographer will check the size of your babies and confirm or move your due date depending on the result. When twins are confirmed, the sonographer should do a chorionicity scan to find out whether or not your twins share a placenta. If the sonographer is not able to determine chorionicity, you should get a referral to a Maternal Fetal Medicine MFM specialist. Twins who share a placenta are more at risk for complications during pregnancy and delivery. Twins who share a placenta are called monochorionic twins.
For many women, especially after 8 weeks gestation, sufficient information about the baby may be obtained with transabdominal ultrasound only. However, in the early pregnancy, the developing embryo is very small at 6 weeks gestation, the baby is only mm long and a transvaginal ultrasound may be required to get a better image of the baby. Transvaginal ultrasound is safe and commonly performed during all stages of pregnancy, including the first trimester.
Pettker, MD; James D. Goldberg, MD; and Yasser Y. This document reflects emerging clinical and scientific advances as of the date issued and is subject to change.