MSAFP Blood Test Screens for Neural Tube Defects in Pregnancy

Somewhere around your fourth or fifth month of pregnancy, your doctor may offer you a blood test you hadn’t heard of before: MSAFP. It measures alpha-fetoprotein (AFP) in your blood, and it’s usually done in the second trimester.

Here’s the part worth holding onto: it doesn’t diagnose anything in your baby. What it does is point out which pregnancies might benefit from a closer look, such as an ultrasound or diagnostic testing.

MSAFP screening: an overview

MSAFP screening, short for maternal serum alpha-fetoprotein screening, is a blood test offered during pregnancy. It measures alpha-fetoprotein, a protein made mainly by the developing fetus, that passes into the amniotic fluid and small amounts into the pregnant person’s bloodstream. The result is used to estimate whether the pregnancy has a higher-than-expected chance of certain conditions.

This is a screening test, not a diagnostic one. That means the result can’t confirm your baby has a health condition, and a typical result can’t rule out every condition either. What it does is help your pregnancy care team decide whether a more detailed look, usually an ultrasound, would be useful.

MSAFP may be ordered as a stand-alone test or as part of a second-trimester multiple-marker screening panel. Practices differ by country, health system, and individual pregnancy history. Many pregnancies now also include detailed ultrasound assessment, which is an important part of screening for structural differences.

How MSAFP screening works and who may be offered it

AFP levels change naturally as pregnancy progresses. A laboratory compares the measured AFP level with the expected median level for the same gestational age, then reports the value as a multiple of the median, or MoM. The interpretation may be adjusted for factors such as the pregnant person’s weight, diabetes status, number of fetuses, and the method used to date the pregnancy.

MSAFP screening timing is usually between 15 and 20 weeks of pregnancy. It is often most informative in the middle of that window, around 16 to 18 weeks. Accurate dating matters because even a small difference in estimated gestational age can affect whether AFP appears higher or lower than expected.

A clinician may discuss this screening with people who want second-trimester assessment for open neural tube defects, including spina bifida and anencephaly. It may also be considered when first-trimester screening or noninvasive prenatal testing has already been performed, because those tests do not assess every type of structural condition in the same way.

Whether to have prenatal screening at all is your call. A doctor, midwife, or genetic counselor can walk you through what the test can and cannot show, what follow-up might involve, and how that information fits your values and your pregnancy care plan.

What does the MSAFP screening test detect?

MSAFP screening mainly helps identify pregnancies with a higher chance of an open neural tube defect. These conditions occur when the neural tube, the early structure that forms the brain and spinal cord, does not close completely. Higher AFP levels can be associated with open spina bifida or anencephaly, although detailed ultrasound is needed to assess the fetus directly.

An elevated level can also occur for reasons unrelated to a fetal structural condition. Common explanations include an incorrect due date, a multiple pregnancy, vaginal bleeding, or differences involving the placenta. Less commonly, it may be associated with certain abdominal wall defects or pregnancy complications that require closer monitoring.

Lower-than-expected AFP can be seen in some chromosome conditions when MSAFP is interpreted as part of a combined serum screening panel. On its own, however, MSAFP is not a definitive chromosome test. It should not be used to diagnose Down syndrome or other genetic conditions.

The most useful next step after an unexpected result is usually confirmation of pregnancy dating and a detailed ultrasound. Depending on the findings and personal preferences, the care team may also suggest genetic counseling or diagnostic testing such as amniocentesis.

The procedure: what happens during and after the blood test

MSAFP screening is simple and similar to other routine blood tests. No fasting, anesthesia, or special preparation is usually required. Before the blood sample is taken, the clinician or laboratory may confirm information such as estimated due date, current weight, diabetes history, and whether there may be more than one fetus.

A healthcare professional cleans a small area of skin, usually on the arm, and collects a blood sample with a needle. The draw generally takes only a few minutes. The sample is then sent to a laboratory, where AFP is measured and interpreted in relation to the pregnancy details provided.

There’s nothing to recover from beyond the usual care after any blood draw. Most people go straight back to their day. You might notice mild tenderness, a small bruise, or feel briefly light-headed, but serious complications are uncommon.

The main benefit: it can flag the need for a closer look at a stage of pregnancy when ultrasound and specialist advice are genuinely helpful. The catch is that screening tests can give false-positive or false-negative results, which is why your result should always be read alongside the rest of your clinical picture.

How long does it take to get MSAFP test results back?

MSAFP test results are commonly available within several days to about one week after the blood sample reaches the laboratory. The exact MSAFP results time depends on the laboratory, local processing schedules, whether the test is part of a larger panel, and whether information such as gestational age needs to be checked.

If a result needs review, the care team may contact the patient sooner or arrange a follow-up appointment. This does not necessarily mean that a problem has been found. It often means that the laboratory value needs to be interpreted alongside ultrasound findings, pregnancy dates, or other health information.

If you’re wondering exactly how long your results will take, the clinic or laboratory that arranged the test is the one to ask. They can tell you their usual reporting time and how they’ll get in touch. Ask before you leave the appointment; it’s a perfectly fair question.

What is a normal MSAFP score?

There is no single AFP number that is normal for every pregnancy because AFP changes significantly from week to week. Laboratories usually express the result as MoM, which compares an individual result with the median expected value at that stage of pregnancy. A value near 1.0 MoM is close to the median for that reference group.

Many laboratories treat a value below roughly 2.0 to 2.5 MoM as within the expected range for screening in a single-baby pregnancy, though cutoffs vary. Each lab and care team works with its own validated ranges and adjustments. So please don’t try to interpret your MoM value on your own, and don’t compare it with someone else’s.

A higher or lower value does not establish a diagnosis. Dating differences, twins or other multiples, maternal factors, and laboratory calculations can all change the result. A clinician may recommend ultrasound, repeat evaluation, or referral to a maternal-fetal medicine specialist to clarify what the result means.

Is MSAFP the same as NIPT?

No. MSAFP and noninvasive prenatal testing (NIPT) are different blood tests with different purposes. MSAFP measures a fetal protein in maternal blood and is mainly used to screen for open neural tube defects and, in some settings, as part of broader second-trimester serum screening.

NIPT analyzes small fragments of placental DNA circulating in the pregnant person’s blood. It is primarily used to screen for certain chromosome differences, such as trisomy 21, trisomy 18, and trisomy 13. NIPT is highly accurate for the chromosome conditions it screens for, but it is still a screening test and does not replace diagnostic testing when confirmation is needed.

They do different jobs, so having had NIPT doesn’t automatically mean you can skip MSAFP or the second-trimester structural assessment. A detailed fetal ultrasound still matters. What’s right for you depends on how far along you are, your medical history, local recommendations, and the kind of information you want.

When to seek medical care

People should contact their maternity care team if they have not received expected results, do not understand an MSAFP screen result, or are worried after being told that further testing is recommended. Prompt discussion can clarify whether the result may relate to pregnancy dating, multiple pregnancy, an ultrasound finding, or another factor that needs evaluation.

Urgent medical advice is appropriate for symptoms such as heavy vaginal bleeding, severe or persistent abdominal pain, fluid leakage, fainting, fever, or a noticeable reduction in fetal movement later in pregnancy. These symptoms are not caused by MSAFP screening itself, but they should be assessed promptly during pregnancy.

For abnormal screening results, maternal-fetal medicine, radiology, genetics, and obstetric specialists may work together to plan next steps. Acıbadem Health Point’s multidisciplinary specialists and JCI-accredited hospitals provide diagnostic assessment and pregnancy care for Myomectomy Recovery for International Patients: The Usual Travel Timeline" class="ahp-ilk">international patients.

Frequently asked questions