Prolonged Pregnancy

Term pregnancy: 37-42 weeks from last menstrual period

Postterm or postdates: greater than 42 weeks

Incidence

Preterm: 10%

38-42 weeks: 80%

42 weeks: approximately 10% (3-12% various studies)

Exactly 40 weeks: 5 %

Beyond 43 weeks: 4 % prolonged,

GESTATIONAL DATING

Many patients are erroneously dated

Late ovulation

Poor history

Inaccurate ultrasound (US) changes

US and gestational dating

Don't change dates if variation < US accuracy (gestational age dependent)

Never replace early SOhO EDD with later sono: risks missing IUGR or wrongly diagnosing in large fetus

Fetus: increased likelihood of

Oligohydramnios

Meconium passage/aspiration

Macrosomia/shoulder dystocia

Fetal distress: 3x rate of low APGARs

Fetal demise: increases after 41 weeks

Anencephaly

Maternal: 3--4x C-section rate secondary to cephalopelvic disproportion and fetal distress postterm, past due, late

Obstetrician: a leading cause of malpractice litigation in the United States

PERINATAL MORBIDITY AND MORTALITY

A. Decreased amniotic fluid volume (AFV)

1. Peak fluid volume: 1 L at 36 weeks--declines to 900 mL at 40 weeks and 250 mL by 42 weeks

2. Secondary to gradual placental senescence leading to relative hypoxia and

intrafetal shunting

B. Meconium passage

1. 10% term pregnancies, 30%

2. Probably related to mature (3I tract and waning placenta] function

3. Meconium passage with ~, AFV may result in thicker, more tenacious

meconium and much worse aspiration syndrome

4. Macrosomia: fetal weight > 4,500 g

5. Progressively more likely proceeds past due date

6. ~ complications of shoulder dystocia

7. t C-section for CPD

C.Placental