…..Over the last 30 years, ultrasound has changed dramatically in how we evaluate early pregnancy. Transvaginal sonography has allowed us to assess early gestation with better clarity.
…..The gestational sac is the first visible sign of a normal
intrauterine pregnancy. This should be seen with the transvaginal sonogram by 5 weeks after the last menstrual period. The earliest embryonic structure is the yolk sac, and likewise, this can be seen as early as the end of the 5th week. Evaluating the yolk sac is important because it can point to problems in a pregnancy. If it is not present at this early time, or if the shape is irregular or large, this can be the first sign of a nonviable pregnancy.
…..Near the 6th week from the last menstrual period, the embryo should be seen attached to the yolk sac, and fetal heart activity should be noted between the 6th and 7th week. When the gestational sac is approximately 2 cm, an embryo should be seen, and if it is not identified at this time, a blighted ovum is confirmed.
…..There are specific sonographic signs of a problem pregnancy:
- A small gestational sac around the embryo
- If the embryo does not increase in size by 1 mm per day
- A fetal heart beat at a rate of less than 120 beats per minute after 7 weeks of gestation.
…..Let us end this review on a positive note. If a patient has no abnormal symptoms, normal fetal heart activity, and 7 weeks of gestation has been reached, then there is a 99% chance of a successful pregnancy.
…..Let us now start to review how early pregnancy (the first trimester) is evaluated, especially in the case of bleeding.
…..The embryo produces a hormone called hCG very early in the pregnancy, and later the placenta also produces this hormone. Repeating or checking the levels of the hCG every 2 to 3 days is helpful when trying to assess the viability of an early pregnancy and to see if it is normal. At a certain hCG level (between 1200 to 1500), a pregnancy should be visualized by a transvaginal sonographic exam. When serial hormone levels are being followed, it is important to use the same laboratory or else there may be different test kits used at the specific lab, and so the results may not be accurate.
…..The hCG level should have a minimum rise of 50% every 2 days, and some practitioners consider a rise of 66% to better reflect a normal pregnancy. I was taught that the levels should double every 3 days, and this is the formula I have always used.
…..All pregnancies are different, and there is some variability in the rise of hCG in normal pregnancies. There are also some specific circumstances that affect this hormone’s levels:
- If the woman is dehydrated when a test is taken, and on the repeat test she drinks more, the test can be affected
- The level of hCG, which rises so dramatically early in the pregnancy, will begin to level off at about 8 weeks
- In twins and other multiple pregnancies, the numbers can have great variability especially if there is a problem with one of the pregnancies