First trimester ultrasound is becoming more common. Traditionally, early pregnancy ultrasounds were only done if a complication was suspected, but more and more gynecologists are choosing to use first trimester ultrasound to confirm the age of a pregnancy, and simply as a preventative measure.

Pregnancy Due Date

The age of pregnancy is often unknown, either because the mother is unsure which day conception took place, or because her cycle is longer or shorter than 28 days, or variable. The crown-rump length is very accurate for determining the age of a pregnancy. In fact, it is the most accurate age measurement to be taken throughout a pregnancy. It can be used to determine the date of conception. This may be up to several days after copulation, as it can take several days for the sperm to fertilize the egg.


Fetal age measurements taken later in the pregnancy, especially during the second trimester ultrasound, are compared to the first trimester measurement to determine if the fetus is growing too slowly or to quickly, which can be a sign of a greater problem such as maternal diabetes or hypertension.

Early Pregnancy Ultrasound for Viability

Bleeding or spotting during pregnancy is not uncommon. It can be caused by something as benign as a small subchorionic hemorrhage, or it could be the consequence of a miscarriage. First trimester ultrasound is used to determine if a pregnancy is viable by demonstrating a heartbeat. Unfortunately, viability may be questionable between six and seven weeks of age because the embryo may not yet be visible, although it can typically be seen at 6 weeks, 2 days. Common reasons why a healthy embryo may not be seen between six and seven weeks include extra fat on the mother’s abdomen or uterine position. If the embryo cannot be seen, a follow-up ultrasound will be done, usually one week later to allow the embryo and the uterus time to grow.

Corpus Luteum Cyst

The corpus luteum cyst is the follicle that burst during ovulation to release the egg. When the egg is fertilized, the corpus luteum remains on the ovary until about the 12th week of gestation. This is important and necessary because the corpus luteum releases progesterone, a hormone that tells the body that it is pregnant and to act accordingly. The corpus luteum clears up when the placenta matures to the point that it can begin releasing enough progesterone to maintain the pregnancy.

Often, the corpus luteum cyst causes some discomfort or pain, especially when pressure is applied to the area. Pressure may occur from a uterus that bends more toward that side – a normal occurrence – or when the mother bends or twists a certain way. Ultrasound can help determine if the corpus luteum may be the source of pain or discomfort, or whether something more serious is present.

First Trimester Ultrasound Scan

The first trimester ultrasound is very similar to the pelvic ultrasound. The sonographer takes a series of pictures of both the uterus and the ovaries. She also takes measurements of each organ as well as pregnancy-specific measurements: crown-rump length of the embryo, yolk sac, gestational sac, corpus-luteum, and heart rate. You may hear your heartbeat if the sonographer measures the blood flow through each ovary. The heartbeat of the embryo is typically measured using a type of Doppler that does not make sound. This is because the Doppler that does make sound could possibly be damaging to the embryo’s heart, but this is uncertain.

The first trimester ultrasound may take as little as 20 minutes or as long as an hour. This can be influenced by the position of the embryo, the presence of bowel gas, or other factors. The length of the ultrasound has nothing to do with the health of the pregnancy.

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