Postdated or prolonged pregnancy: definition,incidence,causes, diagnosis, risks and management.

Definitions:

 Prolonged, postdates, postterm and postmature pregnancy are some terms which are used loosely and interchangeably .

In them prolonged pregnancy or post dated pregnancy means pregnancy  that has exceeded a duration considered to be the upper limit of normal pregnancy that is above 40 completed weeks or 280 days from the first day of the last menstrual period.

The term postterm  pregnancy means which has exceeded 42 completed weeks or 294 days from the first day of the last menstrual period. Pregnancies between 41 weeks 1 day and 41 weeks 6 days, although in the 42nd week are considered as prolonged pregnancies only as they do not complete 42 weeks until the seventh day has elapsed.

Whereas  postmature pregnancy means pregnancy with a should be used to describe the infant with specific clinical fetal syndrome. As only few infants with prolonged pregnancies will have stigmata of the postmaturity syndrome, using this term to all prolonged pregnancies may falsely imply a pathologically prolonged pregnancy.

Incidence:

As there are many definitions for prolonged pregnancy the incidence varies from 2 to 10%.

When incidence is taken as delivery beyond 42 weeks it is 10%, if it is taken according to the delivered baby’s weight and length it is 2%.

The causes of prolonged pregnancy:

Wrong dates: if the women, having irregular periods with delayed ovulation, or she is not able to recall her last menstrual period correctly, or she used some oral contraceptive pills within 6 months of conception which has lead to irregular ovulation, or she conceived during lactational amenorrhea, in these cases if expected date of delivery is calculated according to her last menstrual period it will come wrong leading to consider as prolonged pregnancy.

By combining the estimated gestational age by the last menstrual period with clinical findings and serial ultrasonography findings the prolonged pregnancy can be diagnosed correctly.

The proportion of births at 42 weeks or longer was 6.4 percent when based on the last menstrual period alone and 1.9 percent when combined with ultrasound findings. By this it can be told that relaying only on the menstrual dates may not accurately  predict the postterm pregnancy. May be because of these variations in menstrual cycle  only small proportion of fetuses delivered postterm will have evidence of postmaturity.

Hereditary factors: hereditary seems to play a role in cases of prolonged pregnancy. According to some studies maternal, but not paternal genes influenced prolonged pregnancy. If  mother had a prolonged pregnancy the chance of daughter having prolonged pregnancy will increase to two- to threefold.

Standard of living: in people belonging to high socioeconomic class and with sedentary lifestyle the chances of prolonged pregnancy are more.

Prior post term pregnancy:  some mothers will have repeated postterm births may be  suggesting some  biologically determined factor behind it. After first postterm birth the incidence of a subsequent postterm birth increases from 10 to 27 percent  and after two prior, successive post term deliveries the incidence further increases to 39 percent.

Parity  and age: in case of elderly multiparae or elderly primigravidae the chances of prolongation of pregnancy are more.

Placental factors: X-linked placental sulfatase deficiency may lead to prolongation of pregnancy.

Fetal factors: anencephaly without polyhydromnios, adrenal hypoplasia may lead to prolongation of pregnancy. May be because fetal hypothalamo-pituitary-adrenal axis cannot function to initiate labor. One concept is that these lead to decreased estrogen levels which will be usually high in normal pregnancy and  reduced cervical nitric oxide release may be a factor.

Diagnosis of prolonged pregnancy:

Prolonged pregnancy can be diagnosed according to the last menstrual period, if the woman is very sure of her dates and had regular periods for at least 3 months before conception and  not used  oral contraceptive pills within 6 months of conception and not conceived during lactational amenorrhea.

It can be diagnosed according to previous regular clinical checkups with well maintained antenatal record.

It can also be diagnosed with serial ultrasound examinations, preferably started early in the pregnancy.

The clinical findings suggesting prolonged pregnancy are:

These are more evident in case of post term pregnancy.

The patient weight checking may reveal stationary or falling weight.

The girth of the abdomen may decrease because of diminished liquor.

Sometimes patient may experience false pain which will coincide with expected date of delivery followed by its subsidence and continuation of pregnancy indicates prolongation.

During palpation the uterus appears as full of fetus because of diminished liquor with hard skull bones.

In vaginal examination feeling of hard skull bones of the fetus through cervix or fornix usually suggest the maturity.

Ultrasonography in detecting post maturity:

From the evidence of early ultrasound scan which will detect the gestational age more accurately diagnosing prolonged pregnancy is better than with ultrasound in third trimester which will have 2 to 3 weeks variation.

 But by using composite biometry which includes BPD(bi-parietal diameter), HC(head circumference), AC(abdominal circumference) and FL(femoral length), in late pregnancy also prolonged pregnancy can be predicted. BPD more than 10.1 cm suggests postmaturity.

The ultrasound in postmaturity may show placental aging with calcification with diminished amniotic fluid index.

Amniocentesis in diagnosing the maturity:

It is generally not used as it is an invasive method.

Following are the amniotic fluid indicators of maturity:

Osmolarity of 250 osmolo/lit.

Lecithin : spingomyelin ratio, more than 2.

Presence of phosphotidyl glycerol in amniotic fluid.

Creatinine > 2 mg/100 ml in amniotic fluid.

Appearance of >50% of orange colored cells when stained with 0.1% of nile blue sulphate.

Optical density difference greater than 0.15 at 650 mµ.

X-ray in detecting post maturity:

In strait X-ray abdomen thickness and density of fetal skull bone shadow, appearance and density of ossification centers at the lower end of femur at 36 to 37 weeks and at upper end of tibia at 38 to 40 weeks will help in diagnosing the maturity. 

Clinical evidence of postmaturity:

Postmaturity syndrome:

The baby: may have birth weight of 4kg and length of 54 cm but these findings are variable, even the baby may have underweight.

The postmature infant presents with characteristic features of wrinkled, patchy, peeling of skin. 

The wrinkling is particularly prominent on the palms and soles.

 Long, thin body suggesting of wasting and advanced maturity.

As the the infant is open-eyed, he appears unusually alert, old and worried-looking.

The nails are typically quite long extending beyond nail beds.

Most of postmature infants are not growth restricted because their birth weight seldom falls below the 10th percentile for gestational age. Severe growth restriction, however, which

logically must have preceded completion of 42 weeks, may occur.

The incidence of postmaturity syndrome noted to be about 10 percent in pregnancies between 41 and 43 weeks. The incidence increased to 33 percent at 44 weeks.

Associated oligohydramnios will increase the likelihood of postmaturity. Among the pregnancies in which the ultrasonic maximum vertical amnionic fluid pocket measured 1 cm or less at 42 weeks, 88 percent of the infants were found to be postmature.

The postterm fetus sometimes continue to gain weight thus a large infant may born at birth.

Continued  fetal growth though at a slower rate is characteristic between 38

and 42 weeks, it will show that  fetal growth continues until at least 42 weeks.

Liquor: will be scanty and may appear in saffron color because of meconium.

Cord : cord may have decreased Wharton’s jelly, so may become vulnerable to compression.

The diagnosis of placental insufficiency:

Clinically : aging of placenta is manifested by excessive infarction and calcification.

Ultrasonography with Doppler: may show absence of umbilical artery end-diastolic frequency indicating fetal compromise.

Placental insufficiency is expected to be the the main reason for establishment of postmaturity syndrome.

The skin changes of postmaturity were due to loss of the protective effects of vernix caseosa.

The placental apoptosis means programmed cell death will significantly increase at 41 to 42 completed weeks compared with that at 36 to 39 weeks. The clinical significance of such

apoptosis is unclear at this time.

Cord erythropoietin levels were significantly increased in pregnancies reaching 41 weeks or

more which may be because of decreased partial oxygen pressure.

The dangers due to post maturity:

Fetal related: 

perinatal mortality:

It is observed that perinatal mortality increases if the expected due date passes.

The perinatal risk index is the cumulative probability of perinatal death multiplied by 1000. The perinatal mortality rate is the number of perinatal deaths with delivery in a given gestational week divided by the total number of births in that week multiplied by 1000.

All components of perinatal mortality, antepartum, intrapartum, and neonatal deaths

were noted to be increased at 42 weeks and beyond. The most significant increase noted in   intrapartum.

The major cause of death in antepartum period is fetal hypoxia because of placental insufficiency it is more in case of  pregnancy with hypertension, elderly patients, with history of bleeding in pregnancy etc.

In intrapartum period asphyxia and intracranial damage can occur because of preexisting hypoxia, prolonged labor with cephalopelvic disproportion due to big baby, non moulding of head and hard skull bones, operative interference, less liquor and decreased Wharton’s jelly leading to cord compression. The rate of cesarean delivery for dystocia and fetal distress was significantly increased at 42 weeks compared with that of earlier deliveries.

In postpartum period: respiratory distress can occur due to meconium aspiration syndrome and atelectasis, which may lead to low apgar scores, hypoglycaemia and polycythemia can be seen. More infants were admitted to intensive care in postterm pregnancies. The incidence of neonatal seizures and deaths doubled at 42 weeks.

Delivery at 38 weeks was associated with the lowest risk of perinatal death.

Mother related:

Increased operative interference and hazards of induction may increase maternal morbidity. But post maturity itself will not cause any harm to mother.

Management of prolonged pregnancy:

Before proceeding for the management of prolonged pregnancy confirmation of prolongation is important. But there is no accurate method to diagnose truly prolonged pregnancies, so all pregnancies judged to be 42 completed weeks should be managed as if abnormally prolonged.

It is generally accepted that antepartum interventions are indicated in management of prolonged pregnancies.

The cases can be divided as uncomplicated and complicated.

In uncomplicated cases:

One method is selective induction that is waiting till spontaneous onset of labor and till that monitoring the well being of the baby by daily fetal movement count and biophysical profile etc. And induction to be done at early evidences of fetal compromise.

Second method is routine induction, in this induction is planned at 41 or 42 weeks depending on the circumstances.

In it the major thing to be decided is whether to intervene at 41 or 42 weeks.

Another is whether labor induction is warranted compared with expectant management using antepartum fetal testing.

One method is to induce labor at 41 weeks if the cervix is favorable.  Antepartum fetal monitoring  is advocated beginning at 41 weeks when the cervix was unfavorable.

At 42 weeks better to induced labor either the cervix is favorable or unfavorable as perinatal mortality is high beyond this period.

Cervical favorability is having considerable impact on management.

In case of favorable cervix induction is done by stripping of membranes followed by low rupture of membranes and oxytocin infusion. In case of thick meconium stained liquor because of placental insufficiency, caesarean section can be opted.

In case of unfavorable cervix prostaglandin preparations can be used to make it favorable then line of action is same as favorable cervix.

The  chances of prolongation of labor to be kept in mind during delivery which may occur because of big baby, poor moulding. Shoulder dystocia can occur. More analgesia and liberal episiotomy may be useful. In case of fetal distress, baby to be delivered quickly either by  instrumental delivery or by caesarean section.

In complicated cases:

 The  management depends on associated complications.

If the associated factors are contracted pelvis or post caesarean section or malpresentations etc elective caesarean section can be opted.

In case of complications like gestational diabetes, pre-eclampsia or eclampsia, Rh-negative pregnancy, bleeding history in present pregnancy  which will lead to placental insufficiency termination to be planned either by  induction or by caesarean section which ever may be safest but pregnancy should not be prolonged.