Prolonged pregnancy
By: Dr:ISHRAQ MOHAMMEDProlonged pregnancy
Pregnancies of 294 days duration or more are defined as prolonged, post-date ,post –Term. Prolonged pregnancy is associated with an increase in perinatal mortality &morbidity in pregnancy which appear to be otherwise low risk .
Incidence of PP:
If we depend on LMP ,the incidence of PP is 10%.If we depend on first trimester U/S , the incidence will decrease to 6%.
PP is increase in first pregnancies , but it is not related to maternal age &the median duration of pregnancy is 2 days longer in nulliparae compared with multiparae .
Women with body mass index of greater than 30 are at increase risk of PP.
AETIOLOGY OF PP.:
1- it is likely that the majority of PP. represent the upper range of a normal distribution .2-Genetic factor might regulate the onset of labor .
3-previos PP .The risk of PP is twice in women with previous PP compared to women with no history of PP .
4- Women with male fetus has an increase risk of PP .
5-Low vaginal level of fetal fibronectin at 39 weeks are predictive of an increase likelihood of PP, this is associated with long cervix .
6-PP could result from variation in the CRH system during pregnancy , such as alteration in the number or expression of myometrial receptor subtypes.
Risks associated with PP.
1- perinatal mortality : there is 6 folds increase in the PMR.
2-there is a 4 folds increase in intra-partum fetal death .
3-there is an increase in early neonatal death .
4-there is an increase in the perinatal morbidity : meconium staining liquor , meconium aspiration syndrome ,neonatal seizures , neonatal sepsis ,brachial plexus injury .
5-there is an increase in birth trauma &shoulder dystocia .
MATERNAL RISKS :
1- increase incidence of dystocia (prolonged labor ).2- increase incidence of operative interventions i.e. caesarean section was significantly more common with PP. The increase was equally due to failure to progress &fetal distress .
3-increase incidence of birth trauma &shoulder dystocia which in turn lead to increase incidence of perineal injury &post –partum haemorrhage .
Antenatal tests in PP :
No single test is effective so combination of methods should be used .1-U/S assessment of amniotic fluid :by measuring the largest vertical pool of amniotic fluid &used as a 1 cm pool depth as the cut –off for intervention . This was subsequently modified to 2 cm to improve detection of growth retarded infant . I has been found that maximum pool depth performed better than AFI in predicting adverse outcome in post-term pregnancy .
However ,this test has poor sensitivity &specificity .
2- Biophysical profile :no sufficient data to show that the biophysical profile is better than any other form of fetal monitoring .The more complex method of monitoring , the more likely to yield an abnormal result , but doesn't improve pregnancy outcome .
3- Cardiotocography: studies have reported very low rates of perinatal loss in high risk pregnancies monitored in this way .
4- Fetal movement counting : this test does not reduce the incidence of intrauterine fetal death in late pregnancy .
5- Doppler velocimetry : no benefit .
Management :
1-U/S to establish accurate gestational age :
This is to reduce the cases of PP .First trimester U/S is associated with lowest rate of PP.
2- active management : induction of labor . Routine induction at 40 weeks would not considered a realistic option for prevention of post-term pregnancy . Women with uncomplicated pregnancy should be offered induction of labor beyond 41 weeks. Women with risk factors should be offered induction at 40 weeks .
Women should informed that there is a small increase in risk associated with continuing pregnancy beyond 41 weeks . Vaginal examination is performed &this could be accompanied by sweeping of the membranes , provided women are warned about the discomfort associated with this &are agreeable to proceed .Membrane sweeping reduces the need for formal induction of labor .The vaginal examination allows the obstetrician to inform the women of the likely ease &success of induction of labor . For women who have previously delivered vaginally &for women with favorable cervix , induction of labor is unlikely to be a difficult process . those with unfavorable cervix , ripening with prostaglandin should be done .
For a patient with a previous caesarean section ,induction of labor is not contraindicated but associated with increase risk of scar dehiscence compared with a spontaneous onset of labor especially with prostaglandins are used