True umbilical cord knot, an emergency during labor.

An umbilical cord knot is an unexpected event that should not change obstetric approach for delivery.

CASE REPORT

A true umbilical cord knot, though in most cases it has no adverse effects, represents an uncertain risk of perinatal morbidity and mortality. We describe a case of acute intrapartum fetal hypoxia, with extraction of the fetus by a c‐section, and the isolated finding of a true umbilical cord knot.

Acute umbilical disorders (by compression, knot, or prolapse) are relatively common obstetric events that could significantly affect perinatal morbidity.1 The reported incidence of true umbilical cord knots is 1.2% for all pregnancies.2

We describe a case of acute intrapartum fetal hypoxia, with extraction of the fetus by cesarean section and the isolated finding of a true umbilical cord knot. We conducted a search in PubMed of the most representative articles containing the keywords: “cesarean section,” “delivery,” “fetal distress,” and “umbilical cord.”

The case involved a 38‐year‐old woman who carried the heterozygous MTHFR C677T and A1298C gene mutations and had experienced 2 spontaneous miscarriages. The patient received prophylactic anticoagulation with 40 mg daily enoxaparin s.c. during pregnancy and 100 mg daily aspirin p.o. in prevention of preeclampsia till 35th week. The pregnancy in question was made possible by assisted reproductive technology and had progressed normally. Labor was induced due to the prolonged pregnancy after mechanical cervical ripening with balloon. During the initial stage of labor (with the cervix dilated 7 cm and at a DeLee fetal station of −3), the fetus began to have recurrent deep atypical variable decelerations with a progressive reduction in the variability and prolonged end‐stage deceleration, which were not medically resolved (Figure 1). An emergent cesarean section was performed in the mother under general anesthesia. The newborn was a male with moderate acidosis (arterial pH, 7.16 [normal range, 7.20 to 7.45]; pCO2, 56.4 mm Hg [normal range, 45 ± 15]; base excess, −8 mEq/L [normal range, 5 to −12]), weighing 3.630 kg and with an Apgar score at minute 1‐5 of 8‐9, with good recovery and requiring no neonatal support. The only finding was a true umbilical cord knot 7 cm from the fetal insertion, with a bloodless cord (Figure 2). The maternal postpartum and newborn developments were satisfactory.

Figure 1

Final fragment of the intrapartum fetal cardiotocographic recording. The arrows indicate the decelerations in the fetal heart rate. *Maternal heart rate recording. **Fetal heart rate recording

Figure 2

True umbilical cord knot

True knots are a seldom investigated finding. The reported risk factors for true knots are an advanced maternal age, multiparity, obesity, anemia, previous spontaneous miscarriages, chronic hypertension, and diabetes mellitus.3

Although we cannot tell exactly when the knot occurs, the maximum longitudinal development of the umbilical cord, combined with the large quantity of amniotic fluid and fetal movements, occurs before the end of the second trimester. Most knots should therefore occur after that point.3 Wharton's jelly protects and isolates the umbilical blood vessels, preventing the early collapse of structures within an umbilical cord knot. Thus, the fetal risk is greater when the cord's diameter is smaller, as in the case of an old knot containing a lower quantity of Wharton's jelly. Moreover, the umbilical blood flow increases over the course of the pregnancy. The obstructive risk of a knot is therefore greater in an advanced pregnancy.4

Although few studies have analyzed these umbilical cord disorders, predisposing factors have been reported, such as an abnormally long or wide umbilical cord,1 amniocentesis, low birth weight, monoamniotic twins, polyhydramnios, and prolonged pregnancy.3 The condition is more common among fetuses of the male sex. There is no apparent association, however, between the condition and assisted reproductive technology.2

True umbilical cord knots often remain hidden prenatally due to their lack of a characteristic ultrasound appearance.4 Unless the knot affects the flow, known as a “cloverleaf pattern”4 or “hanging noose,”3 its visualization is incidental.3

Although knots quadruple the risk of antepartum fetal mortality,2 their progression is unpredictable, and it is unusual for a knot to go taut before the start of labor.3 The acute reduction in umbilical blood flow results in unsettling fetal cardiotocographic readings, particularly atypical variable decelerations in the initial stage of labor (as in our case), and sinusoidal rhythms, as well as meconium‐stained amniotic fluid, with the subsequent increase in labor induction rates and emergency cesarean sections.1

It is difficult to ascertain whether fetal distress, acute fetal asphyxia, or fetal death is attributable to a true cord knot. The study by Maher et al observed no statistical association between the incidence of acidemia among newborns and true umbilical cord knots, which confirms the lack of clinical significance. However, obstructive cord lesions have been linked to fetal thrombotic vasculopathy and long‐term neurological damage.1

The prenatal observation of knots creates an ethical dilemma for obstetricians as to whether to inform the mother of the finding and the risks related to this condition, as well as the potential medical‐legal implications.3 However, a number of authors have upheld the importance of the ultrasound prenatal diagnosis, especially during the third trimester, because it reduces fetal adverse events, establishing a strict check of the fetus’ well‐being during pregnancy and labor.5 According to the study by Airas et al, which analyzed incident cases of true umbilical cord knots, the perinatal results were comparable to those of the general population. The authors indicated that when faced with acute fetal distress due to an intrapartum true knot, the newborns recovered soon after birth, as occurred in our case. Joura et al showed that the presentation and mode of delivery were not significantly influenced by umbilical knots.5 Therefore, the pre‐established approach, with targeted quest and closely monitored, favors induced labor and elective cesarean section due to anxiety, without improving the results.5

Our experience is limited to incidental observations. However, in retrospect and considering the challenge represented by the prenatal diagnosis of knots and the inability to predict its clinical progression and impact, a controlled vaginal birth is the safer option. The actions performed in our case were therefore appropriate.

We can conclude that the presence of a true umbilical cord knot, though in most cases it has no adverse effects, represents an uncertain risk of perinatal morbidity and mortality. The prenatal diagnosis of knots is an exceptional and unexpected event that should not change the planned obstetric approach.

CONFLICT OF INTEREST

The authors declare no conflict of interest.

AUTHOR CONTRIBUTIONS

BDN: Contributed toconception and design, acquisition of data, analysis and interpretation of data, drafting of the manuscript, critical revision of the manuscript for important intellectual content, and supervision. IPL: Contributed to acquisition of data, analysis and interpretation of data, and critical revision of the manuscript for important intellectual content. MRS: Contributed to analysis and interpretation of data, drafting of the manuscript, and critical revision of the manuscript for important intellectual content. FJFB: Contributed to critical revision of the manuscript for important intellectual content, administrative technical or material support, and supervision. CFB: Contributed to conception and design, critical revision of the manuscript for important intellectual content, administrative technical or material support, and supervision.

CONGRESSES

Electronic poster presented in the 26th National Congress Section of Perinatal Medicine of the Spanish Society of Gynaecology and Obstetrics; Murcia‐Spain, 24th‐26th May 2018.