Low PAPP-A in Pregnancy

What PAPP-A is, and where your number came from

PAPP-A stands for pregnancy associated plasma protein-A. It is made by the placenta and measured in your blood as part of the NHS combined screening test, usually alongside the dating scan between 11 and 14 weeks.

The NHS Fetal Anomaly Screening Programme handbook sets out what the combined test uses: "maternal age", "biochemical markers — free beta human chorionic gonadotropin (bhCG) and pregnancy associated plasma protein-A (PAPP-A)", and "ultrasound measurements — nuchal translucency (NT) and crown rump length (CRL)". Eligibility for the combined test is when the crown rump length is "between 45.0mm and 84.0mm".

PAPP-A is never interpreted alone in the screening calculation. The handbook is explicit about its significance: "A decreased level of PAPP-A in the maternal blood in the first trimester is associated with T21, T18 and T13." Levels rise quickly in early pregnancy and continue rising slowly until term, which is why the result is reported as a multiple of the median for your gestation rather than as a raw figure.

The two different things a low result can mean

This is the source of most of the confusion, because low PAPP-A appears in two separate conversations.

First, in the screening result. A low PAPP-A pushes the calculated chance of trisomy 21, 18 or 13 upwards. If the combined test returns a higher-chance result — between 1 in 2 and 1 in 150 under the NHS programme — you will be offered further testing, and the FASP handbook confirms that NIPT is offered following "a higher chance result (between 1 in 2 and 1 in 150) from either the NHS combined or the quadruple test".

Second, and separately, as a placental marker. A low PAPP-A can be reported alongside a lower-chance screening result. In that situation the concern is not chromosomes at all. PAPP-A comes from the placenta, so a low level is treated as a signal that the placenta may not be performing as well as expected, and the follow-up is about the baby's growth.

Many women are told only the second thing and assume the first, or told only the first and never understand why growth scans were added. If your letter is unclear about which conversation you are in, ask directly whether your combined test result was lower-chance or higher-chance.

Why the follow-up is growth scans

Extra ultrasound surveillance for low PAPP-A comes from fetal growth pathways rather than from the screening programme. NHS England's Saving Babies' Lives care bundle sets national expectations for identifying babies at risk of fetal growth restriction, and RCOG guidance on the small-for-gestational-age fetus sets out how risk factors translate into serial ultrasound rather than symphysis-fundal height measurement alone.

In practice this usually means serial growth scans in the third trimester, often from around 26 to 28 weeks and repeated every few weeks, sometimes with umbilical artery Doppler assessment. The exact protocol varies between maternity units because it is set locally within those national frameworks, so the schedule you are given may differ from a friend's in another trust.

NICE guideline NG201 on antenatal care sits underneath all of this as the baseline schedule that the extra scans are added to.

What low PAPP-A does not mean

It does not mean your baby has a chromosomal condition. It is one input into a chance calculation, and the overwhelming majority of women with a low PAPP-A and a lower-chance screening result have babies with no chromosomal condition at all.

It does not mean your baby will definitely be small. It marks a group with a raised risk, which is why surveillance is offered; most babies in that group grow normally.

It is not caused by anything you did. It is a measurement of a placental protein. One thing that does affect the number is smoking: the FASP handbook records that "smoking affects biochemical marker levels, particularly PAPP-A and inhibin" with "a moderately large reduction in PAPP-A levels" in women classed as smokers, and asks for smoking status to be recorded with the sample. Vaginal bleeding, by contrast, does not substantially change the markers — the handbook states that "current evidence suggests that the biochemical marker levels are not substantially changed in a woman with a history of vaginal bleeding".

Aspirin, and why you may or may not be offered it

Low PAPP-A is often discussed alongside low-dose aspirin, because the same placental mechanism links it to pre-eclampsia and growth restriction. Whether aspirin is offered depends on your overall risk-factor profile under the national pre-eclampsia prophylaxis criteria rather than on the PAPP-A result by itself, and units differ in how they weigh an isolated low PAPP-A.

This is a question for your obstetric team rather than one with a single published answer for low PAPP-A alone. Ask specifically whether you meet the criteria for aspirin prophylaxis, and if you are prescribed it, when to start and when to stop. This page does not publish doses.

What to watch for yourself

Extra scans do not replace paying attention between them. Reduced or changed fetal movements are the symptom that most reliably prompts same-day assessment, and they should never be left until the next scheduled scan. Persistent headache, visual disturbance, upper abdominal pain or sudden swelling should be reported urgently as possible signs of pre-eclampsia.

Take the growth scan schedule you have been given and check that the appointments actually exist in the system. Low PAPP-A pathways are one of the easiest things for a busy service to lose track of, and the scans are the entire point of the diagnosis.