What is amniotic fluid?
- Amniotic fluid is the fluid around fetus (Unborn baby in uterus)in which it swims during the course of the pregnancy. This is approximately 98% water.
- In a term pregnancy, total volume of fluid is around 2800 ml
Definition of Oligohydramnios
Abnormally decreased volume of amniotic fluid is called ‘Oligohydramnios”
Oligohydramnios- Water Around Fetus Decreases During Pregnancy.
Anhydramnios- No measurable pocket of amniotic fluid around baby
Source of amniotic fluid
Amniotic fluid is a secretion of fluid from various sources. The main sources are listed below
- Membranes and placenta surrounding baby
- Fetal skin
- Fetal urine production
- Fetal lung fluid
Importance of amniotic fluid
Amniotic fluid serves several roles during pregnancy
- It allows the fetus to have movements in the uterus. This helps in development of muscles and bones of the baby
- Fetus keeps on swallowing this fluid. This helps in development of intestines of the baby.
- It gives space so that fetal lungs can expand. This will help in development of lungs of baby and baby will breathe normally when born
- Fetus draws its blood supply, oxygen and nutrition from umbilical cord. Adequate amniotic fluid is necessary for its free movement and continuous supply.
What are trimesters of pregnancy
- The total duration of pregnancy that is 40 weeks is calculated as 9 months plus one week. Calculation is started from first day of last menses.
- These 40 weeks are divided into three groups
- First trimester- include first 12 weeks
- Second trimester- weeks 13 -28
- Third trimester-29- 40weeks
Diagnosis of oligohydramnios
- Diagnosis is done by doing sonography ( Ultrasound) .Overall quantity of fluid is estimated .
- Colour Doppler studies of umbilical artery will tell if fetus is receiving enough blood supply.
- NST- Non Stress Test- a tracing of fetal heart rate pattern is a good indicator of baby’s well being
When does it happen
When oligohydramnios is detected in early second trimester .
1) By 18 weeks of pregnancy fetal kidneys are the main source of amniotic fluid. Those fetal abnormalities which will result in decreased fetal urine production as the kidneys are not properly formed or there is obstruction in passage of urine will give rise to oligohydramnios. A few major genitor-urinary abnormalities are
- Renal agenesis (non formation of kidneys )
- Multicystic dysplastic kidney ( Kidneys are malformed and have multiple fluid filled structures in it)
- Polycystic kidneys ( Kidneys have multiple cysts)
- Bladder outlet obstruction ( urine is forming normally but can’t come out of bladder as the outlet has obstruction)
- Posterior urethral valves ( urethra is the tube like structure which will let the urine come out of bladder- if there are valves preventing the urination-oligohydramnios develops)
- Urethral atresia- urethra is not completely formed
2) Rupture of bag of membranes which is around the fetus. This will clinically present as watery discharge from vaginal. There may be bleeding too. Later on patient may complain of pain in lower abdomen which is associated with uterine contractions.
Mid pregnancy onset
When decrease in amniotic fluid happens in late second trimester or early third trimester.
In these times , oligohydramnios is associated with
- Suboptimal fetal growth- IUGR ( Intra Uterine Growth Retardation )
- Placental abnormality-Placenta is not working at its optimal level and blood supply in it is less.
- Pregnancy induced hypertension ( High BP ) clinically known as PIH
Post term pregnancy onset
When the pregnant woman has crossed the due date, oligohydramnios may set in
It is usually because of suboptimal functioning of placental surfaces.
Some medicines if taken in pregnancy for a long time will lead to development of oligohydramnios
All medications in pregnancy should be taken on advice of expert gynaecologist
Prognosis (outcome) of oligohydramnios
If pregnancy is complicated by oligohydramnios-the baby will suffer many abnormalities
Potter’s syndrome- it is a combination of three features
- Limb contractures- hands and legs may have abnormal shape
- Compressed face- face looks abnormal
- Death of fetus from pulmonary hypoplasia- the lungs are underdeveloped and do not support the life of baby
Many other adverse fetal effects are also associated with oligohydramnios
- Fetal malformations
- Stillbirth- a dead baby is born
- Preterm birth
- Increased chances of Cesarean delivery
- Low birth weight of the newborn which will require care in NICU- Neonatal Intensive Care Unit
- Neonatal death- baby expires soon after being born
- Meconium aspiration- baby passes stool even before it is born. This fecal matter/ stool (Meconium) is ingested by the baby and chokes up the respiratory tract, hence leading to difficulty in breathing after being born.
Management of oligohydramnios
- Management of oligohydramnios requires close fetal monitoring by available diagnostic modalities like sonography and NST
- Medicinal support to increase the blood flow to uterus and baby and to help the fetus gain weight. These medicines have limited effectiveness.
- Timely delivery of the baby as soon as the maturity of the baby is achieved.
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