Preterm birth

Question 1

What is the PTB rate in the US?

Answer 1

11-15%

Question 2

What is the breakdown of spontaneous vs indicated preterm births?

Answer 2

• Spontaneous PTB account for ~60% of PTB; indicated = 40%
  o Indications: (1) PEC (2) IUGR

Question 3

What are the potential pathophysiological changes that can cause PTB?

Answer 3

• Heterogeneity of spontaneous PTB (60%)
  o Pathway:
   Premature activation of fetal HPA axis (stress, > 30 weeks)
   Genital tract ascending infections ( < 30 weeks)
   Decidual hemorrhage/ischemia (smoking, drugs, thrombophilias)
   Uterine overdistension (multiple gestations, polyhydramnios)

Question 4

What is the recurrent risk of PTB with history of PTB? What about for short cervix

Answer 4

• Past OB history:
  o 1 previous PTB = 17-50% recurrence risk
  o 2 previous PBS = 28-70% recurrence risk
  o Problem: up to 50% population are nulliparous
  o The earlier the GA of PTB in the previous pregnancy, the higher the risk in the following pregnancy
• Short cervix: 5 fold increased risk of PTD
  o Abnormal cervical lengths <25mm (10%ile)
• fFN: sensitivity 82%; specificity 82%
  o protein released when there is chorio-residual separation; use after 24 weeks

Question 5

What are the types of cervical cerclage?

Answer 5

Type of cervical cerclage:
- 1) History – indicated
o Beneficial only in women with a history of > or = 3 second trimester losses/PTB
- 2) Physical exam-indicated
o Bulging membranes at 18-26 weeks
- 3) Ultrasound – indicated
o Mostly benefit high risk women with mid-trimester CL < 25mm (77% reduction in PTB rate)
- Women with prior SPTB should be offered 17OHP starting at 16 weeks and then, if CL < 25mm at < 23 weeks, then place cerclage
- Twins? Retrospective reviews found cerclage may help if Cx L < 1.5cm
o RCT have found no effective treatment; cerclage or 17OHP may be harmful if short cervix