The second trimester is typically the quietest. The risk of miscarriage has generally passed. Nausea and vomiting is usually improving, or has resolved, and women generally feel quite well. If travel must take place during the pregnancy, this is usually the best time.
Important diagnostic tests take place during the second trimester. Prenatal genetic screening and testing is often completed early in the second trimester and the detailed ultrasound will take place between 19 and 21 weeks. Women are usually checked for gestational diabetes towards the end of the second trimester.
Prenatal Genetic Screening
Women doing the SIPS or the IPS test will be completing Part 2 of their bloodwork between 14w0d and 20w6d (ideal 15w0d-16w0d).
Women doing the IPS will be having their nuchal translucency (NT) ultrasound between 11w0d and 13w6d (ideal 12w0d-13w3d).
The NIPT can be done in the second trimester, if it was not done in the first. This scenario occurs when the SIPS or IPS tests are positive, in which case the NIPT will be MSP-funded.
PRENATAL GENETIC TESTING
Amniocentesis is a test done to diagnose chromosomal/genetic conditions. It is an invasive test, which involves the insertion of a thin needle into the amniotic sac to obtain a small amount of fluid. It carries a risk of pregnancy loss of approximately 1 in 200. As such, it is reserved for high risk situations. The eligibility criteria change frequently. Currently, they include:
Women with a positive prenatal screening test
Women age 40 or over (except when donor eggs of a woman under age 40 are used)
NT measurement greater than 3mm
Previous pregnancy with trisomy 13, 18, or 21
Pregnancy conceived with IVF plus ICSI
Amniocentesis can be done as of about 15 1/2 weeks.
Detailed Ultrasound
This is the most important ultrasound of the pregnancy. It takes place between 19 and 21 weeks. It assesses the details of the baby’s anatomy and organ systems. The sex of the baby can usually be determined, if desired. The baby’s growth is also assessed.
The location of the placenta is determined. If the placenta is covering the cervix, this is called placenta previa. Special precautions will be outlined and ultrasound confirmation will take place in the third trimester.
Gestational Diabetes Screening
Diabetes of pregnancy, or gestational diabetes (GD) occurs in women predisposed towards diabetes, when the placenta secretes hormones that increase resistance to insulin. Women generally cannot control whether or not they will develop gestational diabetes, but, once gestational diabetes is diagnosed, diet and exercise are very important in its management. Some affected women will also require treatment with insulin injections. Untreated GD can lead to multiple pregnancy complications, the most notable being fetal macrosomia. This is when the baby grows too large. It can cause difficulties with delivery, in addition to other concerns.
The check for gestational diabetes generally takes place between weeks 24 and 28, but women at higher risk may have an initial screen done earlier, in the first trimester.
Checking for GD at 24-28 weeks is done with an oral glucose tolerance test (GTT), where blood sugar levels are tested after the administration of a sweet drink. The OB will recommend one of two approaches.
The 1-Step Diagnostic approach involves a 2-hour test. Women fast for at least 8 hours (water is permitted) and are given a sweet drink (75g). Their blood sugar is tested before the drink, after one hour, and after two hours. If any of these blood sugar levels is above cut-off, GD is diagnosed, and a referral is made to the diabetes clinic for management. Women will be given advice regarding diet and exercise and will be provided with a glucose meter to monitor their blood sugars. They will report back to the clinic regularly, and insulin will be prescribed to women who cannot adequately control their blood sugar levels with lifestyle modification alone.
In the Screening and Diagnostic 2-Step approach, women are given a sweet drink (50g) and their blood sugar is tested one hour later. Fasting is not required. If the blood sugar is above cut-off, they must then do the 2-hour diagnostic test described above.