Just as research has shown that SGA (small for gestational age) or IUGR (intrauterine growth restriction) fetuses are at increased risk for poor outcomes, including low APGAR scores at birth, NICU admission or stillbirth, a small placenta is also a risk factor that has been linked to a greater likelihood of poor outcomes. Similar to SGA/IUGR fetuses, fetuses with placentas less than 10th percentile should be candidates for higher levels of monitoring in the course of prenatal care, in order to help make a fully informed decision about when the best time is for a baby to be born. In spite of the importance of placenta size, placenta volumes are not routinely measured by most prenatal care providers today.

Fetuses of any size can have a small placenta, and research has shown that small placentas are a risk factor for stillbirth, independent of fetal size. Unfortunately, there is a common misunderstanding we hear when a provider says they are monitoring the growth of the fetus, and therefore they do not need to monitor the placenta size. This is incorrect. In other words, just because fetal size is correlated with placenta size in a large data set, this does not mean that every individual fetus has a placenta size that matches the fetus’ growth. When a placenta is small, sometimes a fetus will decrease its growth to match the small placenta. Other times a fetus does not slow its growth to match the smaller placenta, and becomes at risk for outgrowing the oxygen supply the small placenta can provide. These large fetuses with small placentas are at an increased risk of stillbirth, especially at full term, as the F:P (fetal:placental) ratio usually reaches its maximum at or near term.

Dr. Jenn Hutcheon examined a large population of births in Canada(n=87,600), and found that 17% of all stillbirths were potentially attributable to small placentas. Dr. Harvey Kliman estimates 30% of the stillbirth cases he examines are due to undetected small placentas, many of which were originally diagnosed as an unknown cause of stillbirth. Many (though not all) of these stillborn babies were at or near full term when they outgrew a small placenta, when the fetus is growing rapidly at the end of pregnancy. Based on the 17% number from Dr. Hutcheon, we estimate that 4,420 stillbirths per year in the United States are attributable to undetected small placentas, and potentially half a million globally.

Research has shown that large placentas for gestational age are also associated with poor birth outcomes. Large placentas are associated with gestational diabetes, which is well established as a risk factor for both the fetus and mother. Studies indicate that altered growth of the placenta is a predictor of adult onset diseases including cardiovascular disease, hypertension and diabetes. (Janthanaphan et al., 2006)

Yes and no. Placental insufficiency is a bit of a “catch all” diagnosis, and quite vague. What causes the insufficiency? A small placenta is one cause of placental insufficiency, but other causes include abruption, infarctions, malperfusion, and hypermaturity. An insufficient placenta is sometimes diagnosed in time to prevent a stillbirth when additional symptoms present, like preeclampsia or IUGR. Yet a healthy fetus and mother can be at risk for a small placenta stillbirth, with no other warning signs that the fetus is at risk. So while a small placenta is one reason for placental insufficiency, it is currently much more useful in clinical practice to detect and prevent this subset of fetuses who are at higher risk of stillbirth than generally scanning for "placental insufficiency". There are many other reasons why a placenta can fail or be considered insufficient, and they are of course also important to monitor when possible. Research is ongoing to develop methods to directly monitor placental sufficiency in real time. While we are excited about the potential this research holds, we are not aware of any that are ready for use in clinical practice right now.

Estimated Placental Volume (EPV) is a simple measurement that can be done while a fetus is in utero to estimate the size of its placenta. It requires 3 measurements (width, height, and thickness) that can be entered into a formula to determine the volume of a placenta in cubic centimeters. This can be used, along with the gestational age of the fetus, to determine the volume of this placenta compared to other fetuses at the same gestational age.

EPV is very simple. A sonographer, doctor, or nurse midwife trained in EPV can take the three measurements in less than 1 minute using a standard 2D ultrasound as a part of routine prenatal care ultrasounds. There is no risk to the fetus as this is not an invasive procedure. The app to calculate the placenta's volume is free; find it on the App Store as "Merwin's EPV Calculator" and linked on this site's How to Measure the Placenta page.

We recommend everyone is screened as part of ultrasounds during routine prenatal care (beginning at the 20 week anatomy scan and every 3-4 weeks after), and particularly in the third trimester, because placentas can stop growing, there may be no symptoms before the fetus dies. Factors associated with an increased risk of a small placenta may include a small placenta in a prior pregnancy, patients with a history of perinatal loss, decreased fetal movement, low fundal height measurements when amniotic fluid and fetal growth measurements are normal, history of macrosomia, IUGR, dehydration, and a history of blood clotting disorders.

Probably not. A standard ultrasound includes little information on the placenta, despite the fact that the placenta is essential for the survival of the fetus. Typically, the location of the cord insertion and placenta location within the uterus are examined. Even most high-risk prenatal care providers do not measure or examine the size of a placenta as part of their decision making about when a fetus should be delivered, despite the fact that many stillbirths result from conditions affecting the placenta and 17% of all stillbirths are attributable to undetected small placentas (Hutcheon).

Good question! Here are some of the responses we’ve heard:

”But I can’t intervene and deliver every baby who has a placenta that’s less than 10th percentile.”

A: We agree! EPV is just one tool in the toolbox, not a final determination of when a baby should be born. It is helpful to flag fetuses at higher risk who could benefit from increased monitoring. Important subsequent questions a provider should ask include: How much smaller than 10th percentile is this placenta? Smaller placentas come with higher risks of stillbirth. How large is the fetus, and what is the F:P (Fetal:Placental) ratio? A 10:1 F:P ratio at any point in pregnancy may be a cause for concern. What is the gestational age? If full term, the risks of delivery of the fetus might be small, particularly compared to waiting. Has the mother noticed any decreased fetal movement? Are there any other signs of fetal compromise? Is there reduced cord blood flow? Is there evidence of placenta deterioration? EPV alone is not meant to determine the optial delivery time of a fetus, but can potentially help in deciding the optimal time for a fetus to be delivered.

”Show me the controlled, randomized study demonstrating the benefits of EPV, then I’ll act.”

A: We encourage providers to read the peer-reviewed research that has already been published regarding EPV. These published studies, found in our research archive, show that: 1) EPV can detect small placentas, and 2) small placentas increase the risk of stillbirth. While we would like to see a large-scale, controlled, randomized study to see if EPV implementation can also reduce stillbirths (a step beyond detecting small placentas), we have not yet identified a funding source. One hurdle to funding such a study is that controlled, randomized studies in prenatal care and stillbirth are limited by ethical and cost factors. Studies on pregnant women are restricted because they are a vulnerable population. It is unethical to put women in a control group and allow small placentas to fail. Stillbirth, though far too common at 6/1,000 pregnancies in the US, is uncommon enough that any controlled, randomized study would need to be very large in order to be able to detect any significant difference between groups. Additionally, funding for studies on simple technologies like EPV have been difficult to identify. Funding committees tend to prefer “wow” factor ideas, like genetic analysis, in utero surgeries, or studies using MRI to measure the placenta, even though widespread implementation of these ideas may be difficult or expensive. Moreover, no private company stands to benefit financially from this study. The families who would otherwise have stillborn babies, and their doctors, are the ones who benefit from EPV implementation. In spite of these hurdles, we are open to suggestions on where and how to get this large EPV study funded. If you are a researcher or provider with an idea to fund a large EPV study, please email measuretheplacenta@gmail.com.

”I’ll wait until other doctors are doing it, then I’ll do it.”

A: This response is potentially due to our legal system and providers wanting safety in numbers. If doctors provide the same care as other providers in their area, no matter how insufficient or incomplete this care may be, they theoretically decrease their risk of losing a lawsuit in the case of a stillbirth by saying “I do what any other provider would have done.” If doctors do anything different from the providers around them, potential future plaintiffs could theoretically argue they provided a different standard of care than the norm, and this could put them at greater legal risk. However, progress in prenatal care depends on doctors thinking critically, gathering appropriate data on which to make decisions, and doing the right thing for their patients, regardless of legal systems and backwards incentives.

”I want to see more research first, even if it’s not a fully controlled randomized study.”

A: We direct those inquiries to our research archive. Many doctors will review the existing body of research about small placentas and EPV and conclude they should incorporate this into their practice. To further support these extensive findings, we hope to see even more large-scale and ethically conducted research in the future. However, asking for more research is always an option in the field of medicine. What qualifies as “enough” research to implement a new practice? Many will look at the current evidence base for EPV and small placentas and decide that the risk of not incorporating EPV into prenatal care exceeds the risk of continuing with the status quo of ignoring placenta sizes as a risk factor for stillbirth.

”When ACOG supports EPV, then I will implement it.”

A: We have written to the American College of Obstetricians and Gynecologists many times to ask for their thoughts about EPV implementation. They have never responded. We encourage these prenatal care providers to ask ACOG for a literature review on the link between small placentas and stillbirth and statement on EPV.

Share this website and research archive with your prenatal care provider, and ask them to measure your baby's EPV at all second and third trimester ultrasounds. Your doctor and sonographer need to download the manual and app, and learn this simple process. See our list of EPV providers under Resources, and help us grow it by sharing your provider once they agree to measure EPV.

Yes. Please email Dr. Harvey Kliman (harvey.kliman@yale.edu) and he can give you more information on EPV training options.

We are deeply sorry for the incredible road you are walking. You are not alone. Asking questions about why your baby died can be a part of healing and critical to your future healthcare. Please see the For Loss Families page under Resources. Dr. Harvey Kliman can review your medical records and placenta slides to potentially help you find the answers you need, even many years after a stillbirth. He and his assistant aim to make the process as easy as possible. Visit this webpage (https://medicine.yale.edu/obgyn/kliman/placenta/pregnancyloss/) to submit your health records and placenta slides. On Facebook, the Small Placenta Stillbirth Group is for loss families looking for information about small placenta stillbirths, and to meet other families whose babies were stillborn due to a small placenta.

We are deeply sorry you have also walked this painful road. We would be honored to share your story and your baby on this website. Please email measuretheplacenta@gmail.com for information on how to share your story, or other ways to help if you are interested.