If your baby measures small in pregnancy, it is important to follow your doctor's advice, take any tests recommended, attend all your antenatal appointments, and seek emotional support if necessary.

What does “measuring small” in pregnancy mean?

An unborn baby who measures small is of an estimated weight that puts them in the lowest 10% of babies at that stage of pregnancy. They may be called of small gestational age (SGA). According to the Royal College of Obstetrician and Gynaecologists guidelines, women in the UK should have their baby’s growth checked and their baby’s risk factors for a condition called foetal growth restriction (FGR) assessed at their first midwife appointment. FGR is a condition that means a foetus's genetic growth potential is pathologically restricted.

Not all babies that are small for their week of pregnancy have FGR. Even if you are not at risk of FGR, your baby’s size will be monitored regularly in pregnancy. Sometimes FGR is not identified until later on.

A small baby is typically spotted when the sonographer who performs one of your antenatal ultrasound scans measures the difference between the actual and expected weight of your baby at your current week of pregnancy. The weight you gain in pregnancy, the amount of fluid that surrounds your baby, an electronic check of your baby’s heartbeat (cardiotocography), and a Doppler flow study, which measures blood flow from you to your baby’s vital organs, may also be looked at if your doctor is concerned about your baby’s size.

How do I cope with learning my baby is measuring small?

Learning that your baby is measuring small can be upsetting. Some older relatives may recall a time when a baby was thought of as weaker or more sickly because they were born small relative to the length of a pregnancy. However, it doesn’t always mean that you or your baby has a health problem. They may be small for other reasons, such as you or the baby’s father being small at birth. It is still essential to attend all your antenatal appointments so any size issues can be monitored, and your healthcare team can keep a close eye on your pregnancy. If you are having trouble dealing with any information about your baby’s size, it’s important to talk about it. If you cannot rely on family or friends, a member of your healthcare team should be able to either reassure you or direct you to an appropriate counselling service.

Why is my bump smaller than other women in the same week of pregnancy?

Please do not compare your bump or any other body part to what another pregnant woman develops. Every pregnancy is different, and the size of your bump is not an indication that your baby is any more or less healthy than any other mother’s. Any diagnosis of whether your baby’s size is or could be an issue should be made by a healthcare professional. If you are worried about how big you are getting in pregnancy, call your doctor or midwife rather than googling pictures or looking at other women in your antenatal class.

Does my baby measuring small mean they have foetal growth restriction?

Not every baby that measures small in pregnancy has foetal growth restriction. Some babies are small because they have small parents or for other reasons that are not pathological. Up to one in 12 pregnancies is affected by foetal growth restriction. This is often related to a maternal or foetal health problem, though sometimes the cause is unknown.

Why is my baby measuring small?

Again, it may just be that they are naturally small. Most babies who measure small are born perfectly healthy and will not need extra help.

If a baby has FGR, the cause may not be clear to your doctor. It can be a sign of a number of maternal health issues, such as problems with your placenta, anaemia, preeclampsia, chronic kidney disease, being underweight, poorly managed diabetes, poor nutrition in pregnancy, caffeine consumption in pregnancy, and smoking in pregnancy. The infections toxoplasmosis and cytomegalovirus, a type of herpes virus, can also cause an unborn baby to grow less or more slowly than expected. FGR can also indicate a chromosomal or developmental problem with your baby.

Will I miscarry if my baby is measuring small?

Not necessarily. A baby measuring small in the first trimester can raise concerns about miscarriage, but it could also be a sign you aren’t as far along as your healthcare team thought or because of one of the reasons mentioned above. In most cases, foetuses measuring small result in small but healthy babies.

Is FGR my fault?

FGR is not your fault, and apportioning blame will not help you, your pregnancy, or your baby. Doctors don’t always know why it happens. You can make positive lifestyle choices to prevent FGR, such as avoiding drugs (especially cocaine), smoking, and alcohol, staying active, eating a balanced diet, practicing good food and personal hygiene, and managing your stress levels. However, once FGR has been diagnosed or identified as a risk, the best course of action is to follow your doctor’s advice and attend all your appointments.

How will FGR be treated?

FGR will affect your pregnancy care. Your doctor or midwife will likely make a plan with you for increased monitoring for the rest of your pregnancy and you will likely be offer extra tests.

Plans and tests will vary according to the point in your pregnancy at which FGR was discovered. FGR diagnosed in early pregnancy (defined as before 32 weeks in this context) may involve an extended healthcare team, including doctors who work on your hospital’s neonatal unit or specialise in foetal medicine. Treatment also depends on the underlying cause of your FGR, if this has been identified, or anything that might affect your baby’s growth, if this can be managed.

Concerns related to your baby’s size can influence the location where your doctor recommends you give birth; they may want you to deliver in a hospital with a neonatal unit that can provide extra care if necessary. Delivery by Caesarean section may be recommended if your doctor thinks a vaginal delivery might place too much stress on you and/or the baby. Your doctor may also recommend that your baby be delivered before their due date. In general, however, healthcare professionals will seek to keep your baby in the womb for as long as possible. Nobody can make you deliver in a location or manner in which you do not want to, but your healthcare team will have your health and that of the baby’s in mind when they make such recommendations.

What is conservative management of a pregnancy where a baby is measuring small?

In this context, conservative management simply means having your healthcare team monitor you and your baby more closely during pregnancy. Addressing any modifiable risk factors, such as quitting smoking or eating and exercising appropriately, may also be advised. Please seek medical guidance rather than try to address risk factors independently, and do not take any medication without consulting a doctor first.

If my baby is small for their gestational age or has foetal growth restriction in this pregnancy, will this happen in future pregnancies?

Yes, a previous SGA or FGR baby is considered a predictor of future cases. However, knowledge is power, and if your obstetrician knows what may have caused it in this pregnancy, the information could help you and your family going forward. It is important to share your complete medical history with anyone looking after you when you are trying to conceive or pregnant. Your doctor or midwife is not there to judge you; they will be able to advise you on using what you already know to your and your baby’s best advantage. For example, a woman at risk of preeclampsia and/or placental problems might be advised to take 150mg of aspirin once daily at night from 12–36 weeks of pregnancy to reduce their chance of SGA and FGR.

For more information on managing symptoms in every week of your pregnancy, watch Unii's Pregnancy Journey with Dr. Shree Datta. For more on labour and childbirth, watch Giving Birth with Dr. Keith Duncan.

Antenatal Class Questions: What if my baby is measuring small in pregnancy?

Unii looks at the potential implications of issues with your baby's growth in the womb.