Cervical Insufficiency

Cervical insufficiency (incompetence) is the inability of the uterine cervix to retain a pregnancy in the second trimester in the absence of contractions or labour, resulting in painless cervical dilation and mid-trimester loss or very preterm birth. It accounts for about 1 to 2% of pregnancies at high risk and up to 15% of recurrent second trimester losses.

Causes: congenital (collagen disorders, uterine anomalies, DES exposure), acquired (cervical trauma from cone biopsy or LEEP, dilatation and curettage, mechanical dilatation, previous obstetric cervical lacerations, forced dilation in late termination), and idiopathic.

• Painless cervical dilation in the second trimester, with pelvic pressure, increased vaginal discharge or spotting, bulging membranes, and rupture of membranes
• History of second trimester loss with minimal pain, followed by painless delivery of a living fetus before viability
• Short cervical length (below 25 mm) on transvaginal ultrasound at 16 to 24 weeks
• Associated with intra amniotic infection or inflammation in advanced cases

Diagnosis is clinical (history of 1 or more painless second trimester losses with advanced dilation) and ultrasonographic:

• History indicated: at least 1 prior second trimester loss with painless dilation
• Ultrasound indicated: transvaginal cervical length of 25 mm or less before 24 weeks (with previous spontaneous preterm birth below 34 weeks)
• Physical examination indicated: cervical dilation of 1 to 5 cm with exposed membranes, painless, before 24 weeks
• Exclude contractions, chorioamnionitis (fever, tenderness, leukocytosis, amniotic fluid analysis), bleeding (abruption), fetal anomalies, and infection (vaginal swabs)
• Serial transvaginal cervical length measurement every 2 weeks from 16 to 24 weeks in women with a prior spontaneous preterm birth

• History indicated cerclage (McDonald or Shirodkar technique) at 12 to 14 weeks in women with 3 or more previous second trimester losses or preterm births related to painless dilation.
• Ultrasound indicated cerclage for women with a singleton pregnancy, previous spontaneous preterm birth below 34 weeks, and cervical length under 25 mm before 24 weeks (reduces preterm birth below 35 weeks by about 30%).
• Physical examination indicated (rescue) cerclage for painless dilation at 16 to 24 weeks with intact membranes (exclude infection and contractions first; prolongs pregnancy by about 5 weeks): preoperative indomethacin 50 mg orally (then 25 mg every 6 hours for 48 hours) and antibiotics (cefazolin 2 g IV), with the cerclage placed under spinal or general anaesthesia.
• Vaginal progesterone 200 mg nightly (or 90 mg gel daily) from 16 to 24 weeks until 34 to 36 weeks for short cervix (below 25 mm) without prior preterm birth; alternative to cerclage in some cases; 17-OHPC is no longer recommended.
• Cervical pessary (Arabin) is an option for short cervix in selected cases, with mixed evidence.
• Postoperative: pelvic rest, avoidance of heavy lifting, serial ultrasound, and monitoring for infection; cerclage is removed at 36 to 37 weeks, or earlier with labour, PPROM or infection.
• Contraindications: active labour, bleeding, chorioamnionitis, ruptured membranes (relative), fetal anomalies.
• Transabdominal cerclage (laparoscopic or open) at 10 to 14 weeks or pre-pregnancy for failed vaginal cerclage or very short or absent cervix; delivery by caesarean section.
• Antenatal corticosteroids (betamethasone 12 mg IM, two doses 24 hours apart) at 24 to 34 weeks if delivery is threatened, and magnesium sulfate for neuroprotection under 32 weeks.