Definition:

A term is from the 37th to 42 weeks of gestation. A pregnancy is said to be prolonged when it exceeds 42 weeks of gestation. Most obstetricians result to induction before 42 weeks of gestation.

 

Incidence:

The incidence of post date pregnancy is difficult to estimate because of many factors. Many women are not 100% sure of the date of the first day of the last menstrual period and secondly many obstetricians result to induction of labour before 42 weeks of gestation.

 

Aetiology (Causes):

i)Unknown date of conception: This can be caused either by irregular periods or incorrect date of the last menstrual period. Ovulation usually happens around the 14th day of the menstrual cycle, but if the periods are not regular it does not happen around the 14th day.

 

ii)Hereditary factor: Patients have a tendency for recurrence of prolonged pregnancy in successive pregnancies in the same individual.

 

iii)Illiteracy and uncertain dates: common in many parts of Africa and Asia.

 

Signs and Symptoms of Post Maturity:

There is a fall in the maternal weight after 40 weeks of gestation.

 

The symphysio-fundal height measurement may exceed 42 cm, this is especially true among the black population since engagement of the head does not take place until the onset of labour.

 

On examination there is diminished liquor amnii relative to the . This is noted only with experience.

 

Outline of the management of  post- date pregnancy

 

Reconfirmation of the expected date of delivery( EDD)

 

The gestational age should be reconfirmed if the mother has not delivered by the 40th week of gestation.

 

An ultrasound scan, if done around the 20th week of gestation will be very helpful. The expected date of delivery estimated by ultrasound scan around the 20th week is very reliable.

 

 

Aim of Management of Post Date Pregnancy

The main aim is to prevent stillbirths . Stillbirths around term are not uncommon and can be very traumatizing for everyone involved, therefore most obstetricians resort to intervention after the 40th week. However when to induce labour after the 40th week is controversial .

The obstetrician should see the mother at 40 weeks and take a decision regarding the policy of delivery.

 

After 40 weeks the mother should be told to keep a fetal kick count chart. She should report to the hospital if she does not feel 10 movements in 12 hours, where an immediate CTG should be arranged. If there is any evidence of fetal compromise , the baby should be delivered as soon as possible.

 

Vaginal Examination:

A vaginal examination should be done to assess the favorability of the cervix for induction around 40 weeks of gestation. A membrane sweep at the time of vaginal examination of the cervix will help expedite labour .

 

Useful Investigations in Post Date Pregnancy:

Radiography: X-ray may be helpful, since the ossification center of the cuboid bone of the baby’s hand occurs at 40 weeks gestation. This is rarely used nowadays either due to the danger of radiation or due to the ease of estimating the expected date of delivery (EDD) by a previous abdominal scan at 20 weeks gestation.

 

Complications of Post Date Pregnancies:

There is a Progressive fall in the oxygen saturation in the umbilical vein from 60% just before term to 30 % at 43 weeks of gestation.Therefore fetal hypoxia could complicate post date pregnancies.

Malpresentations like breech is more common in post mature babies.

As described above there is a higher rate of stillbirh in post dated pregnancies.

There is an increased likelyhood of operative intervention like forceps and caesarean section. 

Prologed labour- due to persistent occipitoposterior position and uterine inertia.

Shoulder dystocia relatively common in post date pregnancies. 

References:

Textbook of Obstetrics for Medical Students Volume 2-2nd Edition by Akin Agboola. et al M.D, F.R.C.O.G, F.W.A.C.S, F.M.C.O.G.

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