SECTION 2:POST-TERM PREGNANCY

1. Cause

1.1 The imbalance of the proportion between estrogen and progesterone

1.2 Cephalopelvic disproportion

1.3 The fetal abnormalities

1.4 The genetic factors

1.5 High prepregnancy body mass index

2. Diagnosis

2.1 Clinical manifestations

2.1.1 Symptoms: 42 weeks of gestation or greater but still not delivering.

2.1.2 Different scenarios: （1）normal growth with: normal fetal size. （2）Fetus continues to grow resulting in macrosomia leading to disproportion and dystocia. （3）insufficient placental blood perfusion leading to decreased placental function, fetal hypoxia and lack of nutrition, this results in fetal growth restriction. And a dysmature baby being small, under-nourished and asphyxiated.

2.2 The auxiliary examination

The electronic fetal monitor testing; ultrasound examination of fetal umbilical artery blood S/D ratio; urine estrogen and creatinine ratio （E/C）; amniotic membrane mirror check; function of the placenta : fetal movement counting,NST , OCT or CST, fetal biophysical score.

3. Impact on the mother and baby

3.1 On the maternal effect: the rate of operative labor and maternal birth trauma are significantly increased. Shoulder dystocia is increased.

3.2 The effects on perinatal infant: fetal distress, meconium inhaled syndrome, neonatal asphyxia with increased morbidity and mortality.

4. Differential diagnosis

Wrong dates. Large babies.

5. Treatment

Depends on placental function, fetal size. Cervical maturity helps to choose appropriate method of delivery.

5.1 Termination -condition of cervical maturity; Fetal weight 4000g or higher or IUGR. Fetal distress. Diminished fetal movements. Non reassuring trace on NST. Oligohydramnios （amniotic fluid index ＜ 3 cm）ormeconium stained amniotic fluid.

5.2 Induce labor- when cervical conditions are favourable with Bishop score of more than 7 points. Where Bishop score is ＜7 ripen cervix with prostaglandins and continue induction with oxytocin.

5.3 Cesarean section-indications: Failure of induction;poor descent of presenting part; signs of early fetal distress;Cephalopelvic disproportion: macrosomia; Breech presentation with mild narrow pelvis; Older primipara; meconium stained amniotic fluid.

5.4 Prevent infections

5.5 Electronic fetal monitoring during labour

5.6 Availibility of senior paediatrician for resuscitation at time of delivery.

（易晓芳）