A patient presents for her first initial OB visit after performing a home pregnancy test and gives a last menstrual period of about 8 weeks ago. She says she is not entirely sure of her dates, however, because she has a long history of irregular menses. Which of the following is the most accurate way of dating the pregnancy?
Measurement of the fetal crown-rump length is the most accurate means of estimating gestational age. In the first trimester, this ultrasound measurement is accurate to within 3 to 5 days. Estimating the uterine size on physical exam can result in an error of 1 to 2 weeks in the first trimester. Quantification of serum HCG cannot be used to determine gestational age because at any gestational age the HCG number can vary widely in normal pregnancies. A single serum progesterone level cannot be used to date a pregnancy; however, it can be used to establish that an early pregnancy is developing normally. Serum progesterone levels less than 5 ng/mL usually indicate a nonviable pregnancy, while levels greater than 25 ng/mL indicate a normal intrauterine pregnancy. Progesterone levels in conjunction with quantitative HCG levels are often used to determine the presence of an ectopic pregnancy.
Determination of uterine size on pelvic examination
Quantitative serum HCG level
Crown-rump length on abdominal or vaginal ultrasound
Determination of progesterone level along with serum HCG level
Antepartum Haemorrhage