Reaching the second trimester of pregnancy often brings a sense of relief — for many women, nausea fades, energy returns, and the pregnancy begins to feel more visible and tangible. It’s also a period of important prenatal evaluations, particularly for women who are 35 or older at the time of delivery, a group sometimes referred to in medical contexts as “advanced maternal age.”
Second trimester screening offers additional opportunities to assess the health and development of the baby and can provide information that some families find valuable for planning and decision-making. Understanding what’s available, what each test measures, and how to interpret results in context can help make this part of prenatal care feel less overwhelming.
Why Screening After 35 May Look Different
Certain chromosomal variations — including trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome) — become somewhat more common as maternal age increases. The increase in statistical risk with age is real, though it’s important to note that the absolute probability of an affected pregnancy remains relatively low even at 40, and the majority of pregnancies in women 35 and older involve chromosomally typical babies.
According to the American College of Obstetricians and Gynecologists, all pregnant women — regardless of age — should be offered the option of prenatal screening and diagnostic testing for chromosomal conditions. The ultimate decision about what screening to pursue is personal and should be made in an informed, unhurried way.
The Anatomy Ultrasound (20-Week Scan)
The anatomy scan — typically performed between 18 and 22 weeks of pregnancy — is one of the most anticipated appointments of the second trimester. During this ultrasound, a sonographer systematically images the baby’s anatomy to check the development of major organ systems, including the brain, heart, spine, kidneys, and limbs. Measurements of the head, abdomen, and femur are taken to assess growth and estimated gestational age.
What the Anatomy Scan Can and Cannot Tell You
The anatomy scan can identify many structural abnormalities, but it is not a definitive test — its sensitivity depends on factors including the baby’s position, ultrasound equipment quality, and the experience of the sonographer. Some structural differences are not visible until later in pregnancy, and some may not be detectable prenatally at all. The anatomy scan is a screening tool that can prompt further evaluation, not a guarantee of an unaffected pregnancy.
If the anatomy scan identifies something that requires follow-up, your care provider will explain the finding in detail and describe what additional evaluation — if any — is recommended. Not every finding on an anatomy scan indicates a significant problem; many so-called “soft markers” require further context to interpret meaningfully.
Cell-Free DNA Screening (NIPT) in the Second Trimester
Non-invasive prenatal testing (NIPT) analyzes fragments of fetal DNA circulating in maternal blood and can screen for chromosomal conditions including trisomy 21, 18, and 13, as well as sex chromosome variations. While NIPT is most commonly offered in the first trimester, it can also be performed in the second trimester if it wasn’t done earlier.
NIPT is a highly sensitive screening test — particularly for trisomy 21 — but it is not diagnostic. A positive NIPT result requires confirmation through a diagnostic procedure (CVS or amniocentesis) before clinical decisions are made. Understanding the difference between screening and diagnosis is central to interpreting any prenatal test result.
For women navigating the emotional weight of these decisions alongside the practical ones, exploring resources on managing anxiety during pregnancy and fertility journeys after 35 may offer helpful perspectives.
Amniocentesis: What It Is and When It’s Offered
Amniocentesis is a diagnostic procedure in which a small amount of amniotic fluid is withdrawn from the uterus using a thin needle guided by ultrasound. The fluid contains fetal cells, which can be analyzed to confirm or rule out chromosomal conditions with very high accuracy. Amniocentesis is typically performed between 15 and 20 weeks of pregnancy.
Who Is Amniocentesis Offered To?
Current guidelines support offering all pregnant women the option of diagnostic testing, including amniocentesis. Previously, it was routinely offered specifically to women over 35 based on age alone, but this approach has shifted to recognize that individual risk assessment — based on screening results, family history, and personal preferences — is more clinically appropriate than age as a sole criterion.
The decision to have amniocentesis is deeply personal. Some families value having a definitive answer regardless of what action they would take with the result; others prefer to continue the pregnancy without a diagnostic procedure. A conversation with your OB/GYN or a genetic counselor can help you work through what kind of information feels most valuable for your circumstances.
Understanding the Risks of Amniocentesis
Amniocentesis carries a small risk of pregnancy loss. The commonly cited historical figure of 1 in 200 (0.5%) is increasingly considered an overestimate based on more contemporary data from experienced centers, where the risk may be closer to 1 in 500 to 1 in 1,000. Discussing the procedure-specific risk at your institution with your care team will give you the most relevant information.
Maternal Serum Screening in the Second Trimester
The quad screen — a blood test typically offered between 15 and 22 weeks — measures four markers (AFP, hCG, estriol, and inhibin A) to calculate the probability of certain chromosomal conditions and neural tube defects. While the quad screen has largely been supplemented by NIPT for chromosomal screening at many centers, it remains in use in some settings and is the primary way to screen for open neural tube defects. Elevated alpha-fetoprotein (AFP), in particular, can be an indicator that warrants follow-up with a detailed anatomy ultrasound.
Genetic Counseling: A Valuable Resource
A genetic counselor can provide personalized guidance on prenatal screening and diagnostic options, help interpret results in the context of your individual background risk, and support decision-making in a non-directive way. Genetic counseling is often covered by insurance, particularly for women who are 35 or older or who have had an abnormal screening result. Many women find a counseling session extremely helpful regardless of whether they ultimately pursue diagnostic testing.
Frequently Asked Questions
Do I have to have all the second trimester screens offered to me?
No. Prenatal screening and diagnostic testing is offered — not required. Each test is optional, and you have the right to decline any or all of them without it affecting the care you receive. Making an informed decision about what you do and don’t want to know is a legitimate and thoughtful approach to your prenatal care.
If my anatomy scan is normal, does that mean everything is fine with the baby?
A normal anatomy scan is reassuring and suggests that the major structural systems being assessed appear to be developing typically at the time of the scan. However, it doesn’t screen for chromosomal conditions (unless soft markers are present), and it doesn’t detect every possible condition. It’s one important piece of the prenatal picture rather than a comprehensive guarantee.
What happens if an abnormality is suspected on a screen or scan?
If a screening result or ultrasound finding suggests something requires follow-up, your care provider will explain what was found, what it might mean, and what additional evaluation is recommended. You’ll typically have the opportunity to speak with a specialist before making any decisions about next steps.
Can I have an amniocentesis if my screening results are normal?
Yes. Some women choose to have amniocentesis for diagnostic certainty even with reassuring screening results, because screening results reflect probabilities rather than certainties. The decision is personal and should be made in consultation with your care team based on what kind of information matters most to you.
Key Takeaways
- The second trimester anatomy scan (18–22 weeks) provides detailed structural information about the baby’s development and is a standard part of prenatal care.
- NIPT can be performed in the second trimester if not done in the first; it screens for chromosomal conditions but is not diagnostic.
- Amniocentesis is a diagnostic test that provides definitive chromosomal information; the procedure is optional and the decision to have it is personal.
- Genetic counseling is a valuable, non-directive resource for navigating prenatal testing decisions, particularly for women with abnormal screening results or personal concerns.
- All screening and diagnostic options are choices — no single pathway is right for every family, and your care team can support whatever decision aligns with your values and circumstances.
Medical Disclaimer
This content is for informational purposes only and does not constitute medical advice. Individual health situations vary significantly. Always consult a qualified healthcare provider before making decisions related to your health, fertility, or pregnancy.
About the Author
Emily Carter is a women’s health writer focused on fertility, pregnancy after 35, and sleep changes in midlife. She writes research-informed, non-alarmist content to help women navigate reproductive and hormonal transitions with clarity and confidence.