Few aspects of pregnancy after 35 generate as many questions, feelings, and decisions as prenatal genetic testing. The landscape of available tests has expanded substantially in recent years, moving from a limited set of optional screening tools to a complex menu of options with varying accuracy, risk profiles, and implications. Navigating this landscape can feel overwhelming—and the decision about which tests to have, if any, is deeply personal.
This article provides an evidence-based overview of the main types of prenatal genetic testing available after 35, what each is designed to detect, what the results can and cannot tell you, and questions worth discussing with your healthcare provider. It is intended to support informed decision-making, not to recommend specific testing choices—those decisions are best made in partnership with your OB/GYN, maternal-fetal medicine specialist, or genetic counselor.
Why Genetic Testing Is Discussed More After 35
The primary reason prenatal genetic testing is discussed more frequently with women over 35 is the age-related increase in chromosomal variations in eggs. The most commonly discussed of these is trisomy 21 (Down syndrome), but other trisomies—including trisomies 18 and 13—also increase in frequency with maternal age. According to ACOG guidelines, all pregnant women, regardless of age, should be offered prenatal screening and diagnostic testing options, though the statistical backdrop shifts with age.
It is important to place this risk in context: the majority of pregnancies after 35, and indeed after 40, result in chromosomally typical babies. The absolute risk of trisomy 21 at age 35 is approximately 1 in 350 at the time of conception, rising to around 1 in 100 by age 40. While these numbers are higher than for younger women, most pregnancies are unaffected—a statistical reality that can be easy to lose sight of amid testing conversations.
Screening Tests vs. Diagnostic Tests: A Key Distinction
Understanding the difference between screening and diagnostic tests is fundamental to interpreting results appropriately.
Screening tests assess the statistical probability of a chromosomal variation being present. They do not provide a definitive yes or no answer; instead, they produce risk estimates. A “high-risk” result means the probability has been identified as elevated compared to background risk—it does not confirm a diagnosis. Conversely, a “low-risk” result means the probability is low, but not zero.
Diagnostic tests provide definitive information about the chromosomal makeup of the fetus. They are highly accurate, but they involve procedures that carry a small risk of pregnancy loss—which is a key factor in the decision-making process.
Understanding this distinction is essential for interpreting results and determining whether follow-up diagnostic testing is appropriate for your situation. Connecting with guidance on navigating prenatal care decisions after 35 may help frame these considerations.
Main Types of Screening Tests
Cell-Free DNA Screening (cfDNA / NIPT)
Cell-free DNA screening, commonly marketed as NIPT (non-invasive prenatal testing), analyzes fragments of fetal DNA circulating in maternal blood from around 10 weeks of pregnancy. It screens for the most common chromosomal trisomies (21, 18, 13) and sex chromosome variations, and some panels include additional microdeletion syndromes. cfDNA screening has high sensitivity and specificity for trisomy 21, with detection rates commonly cited above 99% and low false-positive rates—making it one of the more accurate screening tools available.
However, cfDNA screening is still a screening test, not a diagnostic one. False positives occur, particularly for rarer conditions and in certain populations. A positive cfDNA result should prompt a discussion about diagnostic confirmation rather than definitive conclusions.
First Trimester Combined Screening
This approach combines a blood test (measuring two hormones, PAPP-A and free beta-hCG) with an ultrasound measurement of nuchal translucency (the fluid-filled space at the back of the fetal neck) between 11 and 14 weeks. Combined screening has moderate accuracy for trisomy 21 (detection rates of approximately 85-90%) with a false-positive rate of around 5%. Results are presented as a risk ratio and are used to guide decisions about further testing.
Anatomy Ultrasound (20-week scan)
The mid-pregnancy anatomy ultrasound (typically performed between 18-22 weeks) assesses fetal anatomy in detail. While not a chromosomal screening test per se, it can identify structural findings that may prompt further evaluation or genetic consultation. For women over 35, this scan is a standard and important component of prenatal care.
Main Types of Diagnostic Tests
Chorionic Villus Sampling (CVS)
CVS involves sampling a small amount of placental tissue, either through the abdomen or cervix, typically between 10 and 13 weeks. It provides chromosomal analysis and can detect a wide range of genetic conditions. The procedure carries a small risk of pregnancy loss, commonly cited as approximately 0.5-1%, though rates vary by practitioner and center.
Amniocentesis
Amniocentesis involves sampling amniotic fluid through the abdomen, typically between 15 and 20 weeks. It provides chromosomal and, if indicated, additional genetic information. The associated pregnancy loss risk is generally cited as approximately 0.1-0.3% in experienced centers. Many women opt for amniocentesis over CVS due to the slightly lower procedure-associated risk and the ability to wait for cfDNA or other screening results before deciding.
Decisions about diagnostic testing are best discussed with a maternal-fetal medicine specialist or genetic counselor who can explain the specific risk figures for your situation and provide support for the decision-making process.
The Role of Genetic Counseling
Genetic counselors are healthcare professionals with specialized training in genetics and counseling who can provide detailed, unbiased information about prenatal testing options, interpret complex results, and provide support for decision-making in the context of a confirmed diagnosis. Many maternal-fetal medicine practices include genetic counselors as part of their team, and a referral to genetic counseling before or after testing can be enormously valuable.
Frequently Asked Questions
Do I have to have prenatal genetic testing if I’m pregnant after 35?
No—prenatal genetic testing is offered, not required, for all pregnant women regardless of age. The decision whether to test, and which tests to pursue, is personal and may be influenced by your values, what you would do with the results, and your individual risk picture. ACOG recommends that all patients be offered testing options and receive information to make informed decisions. Declining testing is a valid choice, as is opting for screening only or proceeding directly to diagnostic testing.
What does a positive cfDNA / NIPT result mean?
A positive cfDNA result indicates elevated probability of the condition screened for—it is not a diagnosis. Most major health organizations recommend confirmatory diagnostic testing (CVS or amniocentesis) before making definitive conclusions or irreversible decisions based on a cfDNA result alone. False positives occur, and the predictive value of a positive result varies depending on baseline risk and the condition being screened.
How accurate is the nuchal translucency scan for detecting Down syndrome?
When combined with first trimester blood markers (the combined screen), the nuchal translucency measurement contributes to a test with detection rates of approximately 85-90% for trisomy 21, with around a 5% false-positive rate. It is less accurate than cfDNA screening for this specific condition but provides additional information about fetal anatomy and other risk factors.
What is the difference between screening and diagnostic testing?
Screening tests assess probability and produce risk estimates—they do not confirm or rule out a condition. Diagnostic tests (CVS, amniocentesis) provide definitive chromosomal information but involve procedural risks. The choice between them, and the sequence in which they are pursued, depends on individual factors including your risk profile, how you would use the information, and your comfort with the associated risks and uncertainties. A genetic counselor or maternal-fetal medicine specialist can help navigate these decisions.
Key Takeaways
- Prenatal genetic testing options include screening tests (which assess probability) and diagnostic tests (which provide definitive chromosomal results); understanding this distinction is essential for interpreting results.
- Age-related chromosomal risks increase after 35, but the majority of pregnancies remain chromosomally typical—placing risk statistics in context is important.
- cfDNA/NIPT screening has high accuracy for trisomy 21 but remains a screening, not diagnostic, tool; positive results should be confirmed diagnostically.
- The decision to pursue testing, and which tests to pursue, is personal and should be made with full information, ideally with access to genetic counseling.
- Genetic counselors are a valuable resource for navigating complex test decisions and results, and referral is available through most OB/GYN and maternal-fetal medicine practices.
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.