Preterm And Postterm Pregnancies

Question 1

Pregnancy term broad overview

Answer 1

Human pregnancy is 280 days

• 266 days from conception is the official start of pregnancy
• 9 months in total usually

Current convention is to date pregnancy pregnancies in weeks and days: 28 + 4/7

Naegele’s rule: LMP - 3 months + 1 week = estimated due dates

Definitions:
overall preterm: 20 + 0/7 -> 36 + 6/7
- late preterm: 34 + 0/7 -> 38 + 6/7 
- early term: 37 + 0/7 -> 38 + 6/7 
- full term: 39 + 0/7 -> 40 + 6/7 
- late term: 41 + 0/7 -> 41 + 6/7 
- post term = 42 + 0/7 or greater

Question 2

Risk factors for preterm birth

Answer 2

History

• prior preterm birth (strongest risk with earlier GA at delivery)
• cervical procedures
• periodontal disease

Prenatal care

• UTI or asymptomatic bacteriuria
• cervical length < 25mm on mid-trimester US
• scant prenatal care

Lifestyle

• smoking
• drug use
• BMI < 19.8
• short interpregnancy interval

Question 3

Screening measurements for preterm birth

Answer 3

Transvaginal cervical US with an empty bladder

• smaller cervix = greater risk for pre or posterm
• internal -> external os > 2.5 cm = ideal
• *DONT use:
• fetal fibronectin
• home uterine contraction monitoring
• bacterial vaginosis testing

Question 4

Prevention of preterm brith

Answer 4

interventions are only limited to a personal history of spontaneous preterm birth

1) progesterone supplementation started at 16-24 weeks
- can be vaginal 100-200 mg
- 17-hydroxyprogesterone caproate (17-OHP) weekly

2) cerclage
- transvaginal cervical length screening every 2 wks starting at 16 weeks
- transvaginal length is <25 mm = do cerclage

Question 5

Posterm pregnancy epidemiology

Answer 5

Occurs in 5.5%

Associated with complications:

• acrosomia
• gestational diabetes

Prevention:

• accurate estimation of GA is crucial to catch this
• need to induce labor before 42 weeks