Scans that are needed after second trimester
Knowing the number and types of scans that a pregnant woman needs to undergo during their pregnancy can help them prepare mentally for it. Though the most important scan during your pregnancy is the anomaly scan that is offered at 20 weeks or half-way through your pregnancy, one might have to undergo further scans if they have had complications in their previous or present pregnancy.
Usually, a doctor keeps a track of the growing baby by measuring the fundal height, the distance between the front of your pelvis to the top of your womb, your weight, and the baby bump. They would record your blood pressure regularly. They would measure your insulin levels once in the starting and if you are not prone to developing diabetes or gestational diabetes, then once towards the end. However, they might opt for blood and urine samples to keep an eye on blood levels and infections. If they do detect a problem with any of these tests, they might ask you to undergo a scan, but only as a secondary level test to check on something particular.
If your doctor feels that the measurement of the baby bump and the fundal height do not match or are not as expected, then they might ask you to take the growth scan. You might also be asked to take a scan, if your doctor feels that there is more amniotic fluid than normal. Other reasons for asking you to opt for a scan could include:
Monitoring position of the baby (especially if breech), placenta, and umbilical cord
Checking on twins, triplets or other multiple births
Screening the working of the heart and placenta
A point to note here is that your doctor would not ask you to take the growth scan if the baby seems bigger, but the rest of the symptoms of the pregnancy are normal. This is because once the third trimester starts, the baby takes on an individualistic shape and size. They no longer conform to general rules and develop as per their genes. Also, as they grow, it becomes more and more difficult to measure them.
A growth scan shows how the baby is growing, by measuring their blood flow, checking their movements and measuring them. Baby movements include things like stretching, flexing, moving arms and legs, wiggling toes and fingers, opening and closing hands and moving tongue and lips. Inability to do these indicates a lack of oxygen, increasing the chances of a premature delivery.
What a growth scan would not show is the baby weight, source of bleeding, if any, or the correctness of the due date.
Though ultrasound scans are absolutely normal, with no side effects for either the mother or the baby, be assured that your doctor would recommend these only when they are medically absolutely essential.