When a pregnancy is prolonged beyond the usual period of gestation, it is considered to be postmature or overdue. Before the midwife can diagnose postmaturity, he or she should know the accepted average duration of pregnancy and should also be able to calculate the expected date of delivery.
The average duration of a normal pregnancy is 280 days or 10 lunar months. The expected date of confinement is calculated from the first day of the last menstrual cycle. This is done by adding days to the date of the first day of the last menstrual cycle and adding nine calendar months.
What is prolonged pregnancy?
Prolonged pregnancy is the elongation of pregnancy beyond term or beyond the normal duration (38-42 weeks) counting form the first day of the last normal menstrual period.
A pregnancy that has gone beyond 280 days is known as postmature or prolonged. Usually, in the absence of other complications, the obstetrician waits until the pregnancy is 290 days or more before action is taken.
What are causes of prolonged pregnancy?
Post-term pregnancy is associated with the following factors:
- Maternal age (over 40 years)
- Previous history of prolonged pregnancy
- Obesity/high body mass index(BMI)
- Family history of postmature pregnancy/genetic factors
- Primiparity
- Cephalo-pelvic disproportion
- Male gender of the fetus
- Idiopathic
Ways of estimating the gestational age
- History taking: taking the date of quickening then add 20 weeks. In multiparity, quickening is experienced much earlier (16—18 weeks or 4—5 months); and in primip, it is experienced between 20—22 weeks (5—6 months).
- Abdominal examination (fundal height estimation): this is reliable if the woman books early, that is , on missing the first or second period. This is done using tape which is measured from the fundus to the symphysis. The measurement gotten in centimeter is approximated to be in weeks, e.g. 22cm = 22weeks gestation. An experienced midwife can do the same with finger step count.
- Vaginal examination: check for Hegar’s signs and bimanual vaginal examination usually done in early pregnancy around 8th weeks. In Hegar’s sign, the fingers (index finger and middle finger) of one hand are inserted into the vagina and those of the other hand are placed over the pelvic cavity. The lower part of the uterus feels soft compared with the body of the uterus above and the cervix below.
- Use of ultrasound: ultrasound can be used in early pregnancy to show the following:
- Gestational sac around 5—6th weeks;
- Bi-parietal diameter at different gestational period;
- Crown-rump lengths are shown as follows (a) 6—8weeks = 5cm length; (b) 12weeks = 7cm, etc.
- Radiological evidence: X-ray shows ossification centres in the head and lower limbs. At 36-37 weeks, there is presence of epiphysis or ossification centre in the lower femur. From about 38-40 weeks, there is deposition of ossification centre at the upper tibia.
- Amniotic fluid cytology (Lecthin content of surfactant): Lecthin content of surfactant starts to rise with maturity of fetal lungs but it does not confirm gestational age. It only indicates that the fetal lung is developing.
How to diagnose prolonged pregnancy
The diagnosis of postmaturity is based on the following:
- The duration of pregnancy
- Diminishing amount of liquor amnii
- A drop in the weight of the mother especially in cases in which there has been a steady gain in weight in that pregnancy.
- X-ray examination: A straight x-ray of the abdomen and pelvis showing the fetus will unveil evidence of maturity in some of the fetal bones such as the cuboid and the upper end of the tibia.
- Cephalometry: Measurement of the biparietal diameter by radiological or ultrasonic methods may be of help. A biparietal diameter greater than 9.8cm may be highly suggestive of postmaturity.
- If the membranes rupture, the Nile blue test can be of help. This test involves the staining of the fetal cells with an aqueous solution of 0.1% of Nile blue. All mature fetal cells appear orange when examined after the addition of Nile blue solution. This test, although, not diagnostic of postmaturity (prolonged pregnancy), aids to point to maturity. After delivery, the appearance of the baby, its weight and length and may also be helpful.
Nursing diagnosis of a woman with prolonged pregnancy
- Anxiety related to the unknown outcome of pregnancy evidenced by her tensed facial expression.
- Disturbed sleep pattern related to fear of the unknown outcome of her pregnancy evidenced by going to bed late and waking up early in the night.
- Risk for trauma related to perineal laceration associated with difficult labour.
- Risk for aspiration related to passage of meconium in-utero associated with prolonged labour.
- Risk for impaired skin integrity related to difficult labour associated with big baby.
- Risk for injury (e.g. intracranial injury) related to poor moulding.
- Risk for shock related to birth trauma and placental insufficiency.
Management of postmaturity
The midwife should always refer all suspected cases of prolonged pregnancy to the doctor. The patient is usually admitted to hospital at 10 to 12 days past the expected date of delivery. After ascertaining that the pregnancy is overdue or prolonged, induction of labour is often performed at about 42 weeks of gestation.
In view of accurately diagnosing postmaturity, every effort must be made to ascertain the duration of pregnancy before induction is carried out lest a premature baby is delivered. The date of quickening if remembered by the patient may aid in the estimation of the duration of pregnancy. As a general rule, 20 weeks are added to the date of quickening to obtain a rough estimate of the expected date of confinement.
After induction, supervision of the patient in labour is of vital importance. It should be noted that the infant may be severely asphyxiated at birth. The paediatrician should be informed long before the baby is delivered and arrangements should be made for the transfer of the newborn to the special baby care unit.
How does postmature baby look like?
After delivery, suggestive evidence of postmaturity may be obtained from the birth weight and overall length of the baby. If the baby’s weight exceeds 4kg, postmaturity may be suspected. This is, however, not conclusive. A length of 54cm or more is also highly suggestive of postmaturity.
It is necessary to impress on the midwife that some cases of postmaturity are due to cephalopelvic disproportion. This should be done ruled out before induction of labour is carried out.
The postmature baby sometimes has a typical appearance. It looks old and wizened. Its skin is wrinkled and inelastic (dry peeling skin). The skull bones are usually harder than those of a mature newborn baby.
Complications of post-maturity/prolonged pregnancy
There are two major hazards associated with prolonged pregnancy or postmaturity. It is a known fact that placental function begins to wane from the 38th to 40th weeks of pregnancy.
After the 41st week of pregnancy the longer the fetus remains in-utero the worse the prognosis because of the risk of intrauterine hypoxia. This risk, which is due to diminution in placental function, may be aggravated by pregnancy complications such as pre-eclampsia, hypertension, chronic nephritis and antepartum haemorrhage.
When pregnancy is prolonged beyond 41st weeks, the baby’s size may increases in the absence of placental insufficiency and the increase in fetal head size may cause a difficult labour. This may lead to obstructed labour with all its ugly sequelae.
Hence, two main hazards are recognized in postmaturity:
- Intrauterine hypoxia
- Dystocia
Both of these conditions may bring about an increase in intrauterine death or perinatal mortality rate.
