Evaluation of the Placental Cord Insertion Site on Prenatal Ultrasound: Important but Not the Foremost

The umbilical cord is the channel that connects the growing fetus to the placenta. It is a sinewy vessel that carries vital nutrient to the fetus and removes waste from fetus to placenta where they can be excreted by maternal blood circulation. In ∼90% of pregnancies, the cord implants itself into the right site, the center of the placenta, also known as a “normal” cord insertion; however, sometimes, an umbilical cord is attached to the side instead of the center of the placenta (a marginal cord insertion, MCI), as well as inserting into amniotic membranes on its way to the placenta (a velamentous cord insertion, VCI).[1] As the location of the cord insertion into the placenta is usually included in the second-trimester anatomic scan,[2] the finding of abnormal placental cord insertions (PCIs) may have implications for clinical practice.

Recently, Zahedi-Spung et al[3] determined whether abnormal PCI is associated with small for gestational age (SGA) infants in a retrospective cohort study. The 86 patients with abnormal PCI were matched to 172 patients with normal PCI undergoing anatomic ultrasound with a mean gestational age of 20 weeks. They found that abnormal PCI was associated with an increased risk of SGA (<10th percentile), increased risk of preterm delivery <37 weeks, and <34 weeks compared with controls. There was no difference in rates of cesarean delivery, Apgar's score of <7 at 5 minutes, acidemia, and neonatal intensive care unit (NICU) admission between the two groups. The authors concluded that serial fetal growth assessments in patients with this abnormal PCI may be warranted. However, this study raises some important issues which should be addressed.

This study only presented statistical differences, but no specific observation data, which would reduce the credibility of the study. For example, what were the mean gestational age at delivery and mean birth weight in the two groups? What were the reasons for NICU admission in the two groups? Were there any perinatal deaths in the two groups? Was there significant difference in SGA (<5th percentile) between the two groups? There were 19.8% (17/86) of SGA in the 86 patients with abnormal PCI. Was there significant difference in the rate of comorbidities and tobacco between the 17 patients with SGA and 69 with normal birth weight?

There was no difference in the rates of cesarean delivery in this study. A systematic review reported an association between abnormal PCI and emergency cesarean delivery.[4] In the present study, the rates of cesarean delivery in the two groups were 36.1 and 30.2%, respectively. This means a relatively high baseline cesarean birth rate in their population. Part of this discrepancy may be due to difference in baseline cesarean birth rates between centers.

Based on their findings, the authors recommended serial ultrasounds to detect fetal growth retardation in pregnancies with abnormal PCI. However, there were no significantly high rates of NICU admission and cesarean delivery, and no perinatal deaths. How would serial fetal growth assessments improve the perinatal outcomes? We have no doubt about the association between abnormal PCI and adverse pregnancy-related outcomes, which has been confirmed by a prospective cohort study and a postnatal placental histology study.[5] [6] The key point is: what measures can we take to reduce risks? In clinical practice, once VCI has been excluded, further screening for additional umbilical cord abnormalities and heightened surveillance of pregnancies with MCI may not be necessary.[7] [8] Given the increased risk of vasa previa in the case of a low-lying placenta, follow-up surveillance in cases of MCI involving a low-lying placenta is the focus. Still, care should be taken at delivery to minimize the risk of the cord tearing and to avoid excessive traction prior to placental separation.[9] [10]

In summary, there are still many questions that need to be answered with regard to the association between the abnormal PCI and adverse perinatal outcomes. A future multicenter, large-scale prospective study is needed. In any further researches, care should be taken to assess whether or not the placenta is located in the upper or lower uterine segment to ultimately determine if the variance of VCI makes a difference in safety of both infants and birthing mothers.

Publication History

Received: 21 December 2022

Accepted: 26 January 2023

Accepted Manuscript online:
01 February 2023

Article published online:
24 February 2023

• References

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