How accurate are dating scans in pregnancy

Transabdominal ultrasound will provide a panoramic view of the abdomen and pelvis and is noninvasive, whereas transvaginal ultrasound provides a more limited pelvic view and requires insertion of a probe into the vagina.Transabdominal ultrasound cannot reliably diagnose pregnancies that are less than 6 weeks gestation.The images below will give you an idea of what can be seen and what they look for at each week; of the first trimester.The gestational sac first appears at about 4 weeks gestational age, and grows at a rate of about 1 mm a day through the 9th week of pregnancy.Thus, a simple and accurate way to "date the fetus" in an early pregnancy is to add the length of the fetal pole (in mm) to 6 weeks.Using this method, a fetal pole measuring 5 mm would have a gestational age of 6 weeks and 5 days.In early pregnancies, the actual cardiac rate is less important than its presence or absence.The fetal pole grows at a rate of about 1 mm a day, starting at the 6th week of gestational age.

Below are scan pictures taken during the early weeks of pregnancy.Measurements taken at these early scans will help to; confirm a pregnancy, date the pregnancy and to see any problems that may occur in the pregnancy ( low lying placenta, twins etc.).Scans in early pregnancy are usually performed in the first trimester around 12 weeks.One gestational sac seen with 2 yolk sacs visible inside it Identical (monozygotic) twins.This results from an early embryo dividing into 2 genetically identical embryos.

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