Second trimester tests during pregnancy
The second trimester of pregnancy, the middle period covering weeks 14 to 26, is another busy time for check-ups, tests and screening.
Keeping to this packed calendar is important for the health of the mum-to-be and her baby.
This list covers the most common second trimester antenatal tests for women in good health having a 'normal' pregnancy. Extra tests and screening more often may be recommended by doctors and midwives depending on individual circumstances.
Typically done at 26 to 30 weeks, this is a routine test for pregnancy-induced diabetes, which can result in overly large babies, difficult deliveries and health problems for the woman and her baby. This can be done by either a random blood glucose or a fasting glucose test. If the reading is high, a more sensitive glucose-tolerance test will be recommended, in which the woman fasts for a set period of time (usually overnight) and has blood taken before drinking a glucose drink and again two hours afterwards. Pregnancy-induced diabetes is uncommon, occurring in about 2 to 5% of pregnant women.
Ultrasounds (sonograms) are commonly offered at 10 to 14 weeks, and then again at 18 to 22 weeks, although they may be done at any time during a pregnancy. An ultrasound may be offered for a variety of reasons, including verifying a due date, checking for multiple foetuses, investigating complications such as placenta praevia (a low-lying placenta), or slow foetal growth, or detecting malformations like cleft palate. During the procedure, a device is moved across the abdomen that transmits sound waves to create an image of the uterus and foetus on a computer monitor. Three-dimensional ultrasound provides an even clearer picture of the baby, but they aren't available everywhere and it's not clear whether they're any better than two-dimensional pictures in contributing to a healthy pregnancy or birth.
Maternal serum alpha-fetoprotein (MSAFP) and multiple marker screening
One or the other may be offered in the second trimester. The MSAFP test measures the level of alpha-fetoprotein, a protein produced by the foetus. Abnormal levels indicate the possibility (but not existence) of Down’s syndrome or a neural tube defect such as spina bifida, which can then be confirmed by ultrasound or amniocentesis.
When blood taken for the MSAFP test is also used to check levels of the hormones oestriol and hCG, it's called the triple test. When a marker called inhibin-A is added to the screen, it is known as the quadruple test. The “quad test” significantly increases the detection rates for Down’s syndrome. The test picks up about 75% of neural tube defects and 75%-90% of Down’s syndrome cases (depending on the mother's age), but many women will have a false-positive screening. About 3% to 5% of women who have the screening test will have an abnormal reading, but only a small percentage of those women will actually have a child with a genetic problem.