Fetal movements refer to the muscular movements of the developing baby inside the mother's womb. These may be either reflex movements or elicited in response to noise or touch, at first.
Types of fetal movement
All fetal movements are not alike. At first the mother may feel fluttering movements, which later turn to stronger kicks, and then she notices the baby squirming, rolling or wriggling. There are also hiccup movements. Thus fetal movements are classified as:
Development of fetal movements over time
Before 9 weeks, all the limbs move together, as the nerves are still developing. The embryo arches its head and back.
At 9 weeks yawns and stretches are visible on ultrasound.
At 10 weeks from fertilization, you may see the limbs moving separately, and startle movements.
At 11 weeks the baby can open its mouth and suck its fingers.
By 12 weeks, it is possible to watch the baby swallowing amniotic fluid.
By 13 weeks, the baby vigorously moves arms and legs, in kicks and jabs, and can also respond to skin touch.
At the 14th – 20th week, a great event called quickening occurs. This is the first perception of fetal movement by the mother. Usually felt around 18-20 weeks in first pregnancies, it can be as early as 14 weeks in later pregnancies due to the increased sensitivity of the more relaxed abdominal muscles.
From the 20th - 36 weeks, all types of fetal movements are felt – weak, strong and rolling movements. Tha baby moves all the joints and the spine, ensuring proper joint development. The pattern of movement changes, with weak movements becoming gradually reduced over time, while strong and rolling movements become more frequent.
By 28 weeks, all babies show the startle reflex. Here the baby brings both arms and legs towards the chest when suddenly startled by a loud noise, sudden movement or sensation of falling.
In the third trimester, the baby shows a bicycling movement of both feet, called stepping. This is important in helping to turn the baby upside down for a normal delivery. By this time, the movements are somewhat restricted by the confined space available to the now larger fetus.
Pattern of fetal activity
Fetal movements are not constant throughout pregnancy. From the 20th to the 36th or 37th week, there are mostly weak movements at first. These reduce progressively, but the strong and rolling movements increase. From the 36th or 37th week to full term, these strong and rolling movements reduce again, while weak movements increase.
Rhythms of fetal activity
Fetal movements have their own time-of-day and sleep-activity rhythm. The fetus is often most active between the hours of 9 am and 2 pm, and 7 pm to 4 am. In the last month or so of pregnancy, the baby kicks most during light sleep.
Sometimes the fetus moves less during its sleep cycles. Each cycle lasts 20-40 minutes overall, but may go up to 90 minutes. Fetal rest-activity cycles do not synchronize with the mother's.
Perception of fetal movement
The mother usually feels fetal movements best when she is lying down on the left side, or sitting with her feet up, and concentrating on the movements. When she is busy, she may not even notice them.
Factors which interfere with perception of fetal movement
Other factors which prevent the mother from feeling fetal movements normally are:
- Low volume of amniotic fluid which hinders free movement of the fetus
- Obesity which leads to a thick abdominal wall
- Anterior placenta (this is not valid after 28 weeks), which increases the thickness of the uterine wall at that point
- Smoking
- First pregnancy with tight abdominal muscles
- Drugs such as alcohol, benzodiazepines, opioids including methadone which sedate both mother and fetus
Decreased fetal movements and the kick count
Whenever the mother feels that the baby's movements are reduced, investigation is in order to ensure that the baby is well.
Formerly, fetal well-being was assessed using the “kick count.” This may be done in one of two ways.
- The mother is instructed to sit or lie comfortably, on the left side to maximize blood flow to the fetus, and count ten kicks, keeping track of how long it takes to reach ten.
- Or she is asked to rest on her left side after a normal meal, and count the number of kicks she feels in ten or fifteen minutes.
More than 10 kicks in 2 hours is usually deemed normal. A single episode of decreased fetal activity is not significant in 70% of mothers.
Implications of altered fetal movements
When there is acute fetal distress, often there is a sudden flurry of fetal activity, mostly weak movements. However, with chronic fetal distress, it has been shown that there is a significant reduction or cessation of fetal movements for at least 12 hours before the fetal heart stops. This is called the movements alarm signal (MAS), and indicates impending fetal death. Changes in fetal heart rate follow the MAS within 1-4 days if fetal death does not occur before that
Factors associated with decreased fetal movements:
- Intrauterine growth retardation (IUGR), fetal growth restriction (FGR) or small for gestational age (SGA) babies
- Poor placental function (placental insufficiency)
- Reduced amniotic fluid (oligohydramnios)
- Impending preterm labor
- Fetomaternal hemorrhage
- Intrauterine infections
Fetal outcomes associated with decreased fetal movements:
- Congenital anomalies
- Preterm birth
- Cerebral palsy
- Intellectual disability
- Low birth weight
- Hypoglycemia
- Fetal death
- Neonatal (newborn) death in the early newborn period
- Increased risk of C-section
- Induction of labor
Management
When there is a perception of decreased fetal movements, it is necessary to evaluate the mother's history and to do a physical and other testing. The route of evaluation depends on the presence of any risk factors or whether the mother had a bad outcome in any previous pregnancy.
Usually a cardiotocogram (CTG) and ultrasound is advised. This is a test which assesses the presence of fetal movements as well as the presence of appropriate heart rate responses to the movement. An ultrasound may be necessary if the CTG is abnormal and no previous ultrasound has been done. It will help to assess fetal growth, morphology and the amniotic fluid volume.
Summary
A mother's report of decreased fetal movements is always an indication for fetal and maternal evaluation, irrespective of previous assessments for the same symptom. Repeated episodes require the same intensity of review for factors which may cause or contribute to the symptoms, examination of the pregnant woman, CTG and ultrasound, and testing for fetomaternal hemorrhage (FMH). FMH is usually advised when an abnormal CTG is accompanied by a normal ultrasound. FMH can cause up to 4% of fetal deaths and is often signaled only by the reduction in fetal movements.
Further Reading
Study links air pollution to increased risks of preterm birth and low birth weight