It is common for expectant parents to worry about their baby’s development throughout the pregnancy journey. It is important to have a basic understanding of when to be concerned, and when to wait and see. One of the key indicators of baby’s health is short femur length, which can be detected during the third trimester ultrasound. While this can be an indicator of fetal distress, it is also important to understand when it is likely nothing to worry about. In this blog post, we will discuss when you should be most concerned about short femur length during the third trimester of pregnancy. We will review the basic facts about short femur length, the implications it can have, and when it is a cause for alarm. By understanding when to worry about short femur length during the third trimester, you can rest easy knowing that you are able to properly monitor your baby’s development.
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Is my baby small-but-healthy? Or could it be FGR?
Baby’s with FGR are, by definition, under the 10th percentile for estimated fetal weight and fundal height. If the infant falls short of that threshold, even if they are growing steadily, they may be given the FGR label.
But following these definitions FGR is sometimes over-diagnosed. Longstanding best practices data show that babies in the 3rd percentile or lower are more likely to have an FGR-related complication, and those above the 3rd percentile are more likely to be constitutionally small (based on non-health-related family history of smaller stature).
Babies below the 10th percentile receive standard of care from the UT Southwestern MFM team. In order to prevent overdiagnosis and overmanagement of FGR from placing undue stress on patients, we investigate every possibility. Our goal is to understand:
We use two diagnostic techniques to address these issues: amniotic fluid assessment and Doppler ultrasound examination of the umbilical cord. These analyses may aid in tracing the FGR’s origin and serve as a management guide going forward.
Growth restriction is typically linked to maternal risk factors, fetal anomalies, or placental issues, and occasionally a combination of these conditions. Some risk factors can be controlled, and some cannot.
The following are a few of the most prevalent maternal risk factors for FGR:
Although quitting smoking is difficult, it’s best to do so before getting pregnant. However, it has been shown to be both safe and beneficial for you and the unborn child to stop smoking while you’re pregnant. Your prenatal care provider can help you find efficient, judgment-free smoking cessation or drug use treatment that is intended just for patients who are pregnant.
The most frequent fetal issues that result in FGR are heart conditions. Babies born to mothers who have genetic disorders like trisomy 21 (Down syndrome) frequently have smaller heads than babies born to mothers in the general population. Fetal anomalies are also more frequently associated with stillbirth.
The placenta, like any organ, can develop improperly. Sometimes the umbilical cord is attached to the placenta in the incorrect location, or only one umbilical artery instead of two develops in the cord, resulting in reduced placental blood flow to an otherwise healthy baby.
Rarely, we observe chorioangiomas, a type of placental tumor that interferes with normal function. Placental issues are often the cause of late-onset growth complications.
Ultrasounds are used to make the diagnosis, and most clinics use the 10th percentile cutoff to alert doctors to any potential fetal growth restrictions. The next step is to talk with the patient about her medical history and previous obstetrical experiences.
A patient’s current baby may simply be constitutionally small if her previous child was under 6 pounds at birth but was full-term and healthy. We will be more worried about FGR if this is her first child or if her previous children were larger. To aid in the assessment of placental function in either scenario, we will check the amniotic fluid and umbilical blood flow.
We’ll monitor the baby over the coming weeks if the amniotic fluid and Doppler ultrasound are both normal. If steady growth continues with no new worries, that’s a good sign. The actual delivery date will depend on the baby’s continued growth, the amniotic fluid level, and the results of the Doppler test.
We typically advise having the baby delivered as close to the due date as possible to lessen the possibility that they will require long-term, specialized care after delivery. If the baby is:
Frequently, if there are no additional risk factors, our skilled team can deliver babies safely at 38 or 39 weeks. To reduce the risk of stillbirth, facilities with less experience managing FGR tend to start deliveries earlier. However, a baby typically stays in the neonatal intensive care unit (NICU) for a longer period of time the earlier they are born.
Your care plan will be unique to you because the causes and severity of IUG can vary so widely. Some patients are hospitalized for daily fetal heart rate monitoring. If you are in the hospital, we might advise taking a full course of steroids to support fetal lung development before giving birth.
If you end up needing an early delivery, a cesarean section (C-section) is not required. It is probably safe to try vaginal delivery because many babies are generally healthy aside from their small size. If a baby’s growth is severely constrained or if their Doppler patterns are abnormal, a C-section may be necessary. A discussion with your doctor is always recommended.
FAQ
What if femur length is short in third trimester?
How accurate is femur length in 3rd trimester?
After 26 weeks, all measurement are less accurate. In the third trimester, the variation in both biparietal diameter and femur measurements is +/- 14 to 24 days.
Should I be worry about short femur length pregnancy?
What does it mean if my baby’s femur is measuring small?