Umbilical Cord Abnormalities in the Prediction of Adverse Pregnancy Outcomes

The umbilical diameter is less than 2 cm, grows to a length of 50-60 cm by 28 weeks gestation and contains around 40 helical turns, which are twisted to the left rather than right because of the arrangement of helical muscle fibers in the vessels of the umbilical cord. These twists in the umbilical cord add to the strength of the cord by providing protection and resistance against compression of umbilical vessels. The overall final length of the UC and the number of coils is thought to be determined by the tensile forces due to fetal movements, rate of growth of UA and UV, fetal hemodynamics, distribution of the muscle fibers in the UA and amniotic fluid volume.

One of the common causes of fetal and neonatal adverse outcomes such as stillbirths or hypoxic ischaemic encephalopathy (HIE) is fetal hypoxia. The optimally oxygenated blood is transferred from the maternal blood to the fetus, crossing the placenta and the UC to reach fetal circulation. There are several studies which demonstrate that fetal hypoxia due to placental causes, whether chronic or acute, can lead to reduced transfer of oxygen and nutrition to the fetus. There is evidence from clinical and histological studies that impaired trophoblastic proliferation causes impaired placentation and leads to reduced oxygen transfer to the fetus resulting in preeclampsia (PE), fetal growth restriction (FGR) or stillbirth. However, there is limited and uncertain evidence regarding the contribution of UC abnormalities in the prediction of pregnancies with fetal hypoxia that result in hypoxic adverse outcomes such as HIE and stillbirth. There is need for further research to investigate the causes related to UC as not all hypoxic adverse outcomes have a placental etiology and a significant proportion of pregnancies with FGR, stillbirth and HIE have no ultrasound or histological evidence of impaired placentation, suggesting that there may be other factors in addition to the placenta that lead to such hypoxic morbidity.

There are studies published in literature demonstrating an association between UC abnormalities and adverse pregnancy outcomes such as FGR, PE, stillbirth or adverse outcomes such as caesarean section (CS) for fetal distress; but many of these are postnatal studies based on morphological and histological examination rather than prospective cohort studies carried out in the antenatal period. The few studies that investigate UC abnormalities in prenatal period are retrospective case-control studies with a relatively small sample size. This makes the findings less generalizable and overall difficult to effectively assess the precise contribution of UC abnormalities detected on ultrasound in the prenatal period that can potentially improve management and prevent such adverse outcomes.

This is a prospective observational cohort study carried out at a single center. This study will be conducted in compliance with the study protocol, the Declaration of Helsinki (1996), the principles of Good Clinical Practice (GCP) and applicable regulatory requirements. The study will be reviewed and approved by the Research Ethics Committees (REC) and competent authorities.

At our centre, all women booked for their maternity care are offered 3 routine ultrasound scans in their pregnancy: 11-13 weeks', 20-22 weeks' and at 35-37 weeks' gestation. Pregnancies that are deemed to be at high risk for delivery of a small for gestational age neonate are referred to a specialist placental disorders clinic for closer antenatal monitoring and fetal surveillance. At these visits, we ensure that there is a complete record of their personal, medical and obstetric history and perform an ultrasound scan to assess fetal growth, amniotic fluid and Doppler studies. This prospective study has two parts: first, a prospective observational cohort study in an unselected population and a nested cohort study in a high-risk population. Those agreeing to take part will be offered a patient information sheet and requested to sign a consent form, confirming their willingness to participate.