Is my baby really too small?
To induce or not to induce? Growth restriction. #Behindthecurtain
“Everyone keeps telling me that I need to be induced because my baby is too small, but I was reading online that sometimes that can be because the parents are small and I’m only 5’3” and my boyfriend is only 5’7” and I just want to check if anyone is even taking that into account . . . “
Haley’s* words tumbled through the phone receiver in a rush. I knew she was scheduled for an induction that evening - the charge nurse had been trying to reach her all day with no response. She was finally calling an hour before the end of my shift and it was clear to me that she did not want to be induced. At all.
I waited for her to pause and then took a deep breath.
“You’re right”, I said. “The charts we use to decide how your baby’s weight compares to “average” is based on a single group that definitely doesn’t apply to everyone. And yeah, it makes sense that two tiny people might make a tiny baby.”
“Exactly!”, Haley responded, sounding a little calmer.
“Here’s the thing”, I continued, “there a few other reasons your baby might be small, and some of those reasons can increase the risk of stillbirth. So what I would recommend is that you at least come in tonight so we can check on you and the baby. If everything is normal, we can talk about monitoring to make sure you are both safe, but let’s just make sure there isn’t something going on tonight that would make us worried.”
(*not her real name)
I have this conversation at least once a month, and I did it more when I worked full-time. Haley didn’t arrive at the hospital until after my shift was over so we never met in-person, but here’s a summary of the way I would counseled here if we had.
What is fetal growth restriction (FGR)?
According to ACOG, a fetus is growth restricted if their estimated weight or abdominal circumference is less than the 10th percentile for gestational age.1 (1) In English, if the baby’s weight or the size of their belly is smaller than 90% of babies at their same stage in pregnancy.
The first sign is usually a smaller than normal fundal height (the distance between the top of the pubic bone to the top of the uterus). When this measurement is more than 3 centimeters less than your gestational age in weeks, your provider may recommend an ultrasound to check the baby’s growth.
Why is my baby growth restricted?
I think it’s helpful to think about this in three main buckets
Baby is “constitutionally small”
This is a baby who is growing normally, with a placenta that is working normally, and their normal just happens to be smaller than average. In general, a constitutionally small baby should be small for the whole pregnancy. If your baby was 50th percentile for most of the pregnancy and has suddenly dropped to the 10th percentile, then it is less likely that the baby is just naturally on the smaller side.
There is a problem with the placenta or umbilical cord so that the baby is not getting adequate oxygen and nutrients. This can happen
if the mother has
medical conditions that can affect the placenta like heart and kidney disease, high blood pressure or preeclampsia, malnutrition
infections like malaria, rubella, toxoplasmosis or syphilis,
exposure to certain drugs like alcohol, tobacco, narcotics, and some prescribed medications
OR
if the placenta or umbilical cord have not developed normally.
The baby has a medical condition that prevents them from growing normally like heart disease or a genetic disorders.
Growth restriction is also common in multiple pregnancies (twins, triplets etc.).
What do I do now?
The American College of Obstetricians and Gynecologists (ACOG) and the Society of Maternal Fetal Medicine (SMFM)2 recommend delivering babies with growth restriction at:
38-39 weeks if there is growth restriction in the 3rd to 10th percentile, but no other complications
At diagnosis, and no later than 37 weeks if there is growth restriction in the 3rd percentile, but no other complications.
34 - 38 weeks if growth restriction is present with other findings that are linked to increased risk of stillbirth (low amniotic fluid, abnormal blood flow, or other complications in the pregnancy)
In addition to planning for early delivery, your provider may recommend frequent checks of the baby’s heartbeat, fluid and growth. They may also recommend a high-level ultrasound to check that the baby’s body parts all look normal on ultrasound, or tests for infections and genetic disorders.
OK - but is this really a big deal? Do I actually need to be induced? Isn’t it healthier to wait for my body to go into labor naturally?
The most concerning thing that can happen to a growth-restricted baby is stillbirth (dying in the womb). In cases where a baby is growth-restricted because the placenta cannot adequately delivery oxygen, moving toward delivery might help to prevent stillbirth.
For babies with a normal estimated weight, the risk of stillbirth is less than 1% (fewer than 1 in every 100 babies).
In babies with an estimated weight less than the 10th percentile, the risk of stillbirth is 1.5% (1.5 in every 100 babies, or 3 in every 200 babies of 15 in every 1000 babies).
In babies with an estimated weight less than 5th percentile (smaller than 95% of babies at the same age), the risk of stillbirth is 2.5% (2.5 in every 100 babies, or 5 in every 200 babies or 25 in every 1000 babies).3
The risk of stillbirth is higher if the baby has other abnormal findings on ultrasound (abnormal flow in the umbilical artery).4
You should talk with your pregnancy provider about any other conditions that increase the risks of complications for you or your baby (e.g. high blood pressure, too much or too little amniotic fluid, kidney disease), or if there are any other abnormal findings on your baby’s ultrasounds.
The alternative to induction is watchful waiting (or expectant management). If you choose to wait for natural labor, it is a good idea to continue getting frequent (usually at least twice a week) checks of the baby’s heartbeat (NST), fluid (AFI) and movements (BPP). The baby’s estimated weight measurement is usually repeated once a month. If the testing is normal, it might be reasonable to continue waiting for spontaneous labor. If there are new abnormal or worsening results of these tests, please discuss them with your provider. They may a reason to reconsider induction
It is up to you to decide how comfortable you are with the small, but real, risk of stillbirth.
But doesn’t induction have its own risks? I heard induction can lead to C-sections.
We will go through methods of induction in a different article, but overall, induction methods are safe. A Cochrane review found that inductions of labor after 37 weeks for women with normal pregnancies were not linked to an increased risk of cesarean section.5
In my experience, because growth restriction can be a sign of problems with the placenta, I often tell patients who are getting an induction for growth restriction that there is a chance the baby won’t tolerate labor (induced or natural!) very well and that we may see drops in the baby’s heartbeat with the stress of contractions on an already stressed placenta. Sometimes those drops are concerning enough for me to recommend a cesarean, but if the baby appears safe during labor, a vaginal birth is still the lowest risk option with the easier recovery for mom.
My OB told me my baby was growth restricted so I got induced and now my baby’s weight is normal. What?!
There are a few reasons for this:
Ultrasound is not perfectly accurate - it may produce an estimated weight that is either smaller or larger than the baby’s actual weight.6
Obstetricians and neonatologists/pediatricians use different criteria for normal weight. So you can have an accurate diagnosis of fetal growth restriction from ultrasound, but then a baby who is considered normal weight from a pediatrician or neonatologists perspective.
Haley* came in later that night. Her blood pressures were in the severe rage. She was still not thrilled about the induction (she was hoping to wait for her sister to fly in for the birth), but it turns out both she and her baby were at risk for complications that night. Your situation may be different, but I recommend having open communication with your provider about risk, benefits, and alternatives.
*(still not her real name)
**Disclaimer: I am a doctor, but I am not your doctor. My blog is intended to share information about the recommendations and thought process that guide my OBGYN practice. It is not medical advice and because I am not caring for you I cannot give you any specific recommendations on what to do with your pregnancy. Hopefully this information helps guide a conversation with your pregnancy provider about your specific situation so you can make a decision together. If you have a diagnosis or pregnancy/ladyparts question you would like to read more about, send Dr. A a message or leave a comment below and subscribe to receive new posts!
Fetal Growth Restriction: ACOG Practice Bulletin, Number 227. Obstet Gynecol. 2021 Feb 1;137(2):e16-e28. doi: 10.1097/AOG.0000000000004251. PMID: 33481528.
Martins JG , Biggio JR , Abuhamad A . Society for Maternal-Fetal Medicine Consult Series #52: diagnosis and management of fetal growth restriction: (replaces clinical guideline number 3, April 2012) . Am J Obstet Gynecol 2020 ; 223 : B2 - 17 . (Level III)
Getahun D , Ananth CV , Kinzler WL . Risk factors for antepartum and intrapartum stillbirth: a population-based study . Am J Obstet Gynecol 2007 ; 196 : 499 – 507 . (Level II-3)
Vergani P , Roncaglia N , Locatelli A , Andreotti C , Crippa I , Pezzullo JC , et al. Antenatal predictors of neonatal outcome in fetal growth restriction with absent end-diastolic flow in the umbilical artery . Am J Obstet Gynecol 2005 ; 193 : 1213 – 8 . (Level II-3)
Middleton P, Shepherd E, Morris J, Crowther CA, Gomersall JC. Induction of labour at or beyond 37 weeks' gestation. Cochrane Database of Systematic Reviews 2020, Issue 7. Art. No.: CD004945. DOI: 10.1002/14651858.CD004945.pub5. Accessed 07 July 2024.
Dudley NJ . A systematic review of the ultrasound estimation of fetal weight . Ultrasound Obstet Gynecol 2005 ; 25 : 80 – 9 .