Sunday September 9, 2012
A ‘distressed’ foetus
THE DOCTOR SAYS. . .
By Dr MILTON LUM
Non-reassuring foetal status in labour is usually something that just happens without any foreseeable reason. There is nothing that the mother could have done to prevent it.
THE term “foetal distress” is commonly used to describe the signs indicating that the foetus is not well or not coping well with labour.
However, it is an imprecise and non-specific term as it has poor predictive value in those who are at increased risk. It is often associated with a baby who is born in good condition, as evidenced by the Apgar score (a simple, rapid method that assesses the health of newborns), umbilical cord blood gas analysis, or both. Because of the implications of the term “foetal distress”, inappropriate actions like unnecessary urgent delivery have often been taken.
As such, most obstetricians, acknowledging the imprecision in data interpretation, use the phrase “non-reassuring foetal status” instead.
Challenges to foetal health
Challenges to foetal health can occur in pregnancy, or more commonly, during labour. The reasons are varied, and include insufficient oxygen, biochemical changes, and a sick foetus.
Insufficient oxygen can occur when there is inadequate blood flow to the foetus through the placenta and umbilical cord. It can occur during a contraction in labour.
However, when the uterus relaxes, the blood flow increases. This process is normal, and does not affect a healthy foetus.
However, there are situations in which the blood flow to the foetus is reduced, leading to oxygen insufficiency over time, or suddenly, if it is acute.
The situations include placental insufficiency – in which placental function is less than optimum due to maternal high blood pressure, bleeding in late pregnancy, maternal heart conditions, or growth-retarded or post-date foetuses; excessive uterine contractions in augmented or induced labour; marked decrease in maternal blood pressure, as in heavy bleeding, epidural analgesia and prolonged lying on the back in labour; umbilical cord compression or prolapse; and placental abruption, in which the placenta separates prematurely from the uterine wall, and when twins share one placenta.
Maternal biochemical changes in an ill mother can affect the foetus. This can occur in conditions like diabetes, kidney disease, or reduction of the flow of bile from the liver to the intestine.
The foetus may be unwell for a variety of reasons, like a foetal abnormality, an inherited condition, infection and maternal fever.
The foetus can cope with many of the challenges to its health. However, the likelihood of the foetus being affected is increased if there is maternal diabetes or high blood pressure, multiple pregnancy, or increased maternal age.
Assessment of foetal well being
Foetal movements are the best form of reassurance that the foetus is well. They have been described as a kick or flutter.
Most women are aware of foetal movements at 18 to 20 weeks gestation. The first-time mother may be aware after 20 weeks, and the mother who has been pregnant before may be aware as early as 16 weeks.
The movements are felt throughout pregnancy and during labour. Its frequency and type change with advancing pregnancy. There are periods of maximum activity, and there are periods when the foetus is asleep, lasting 20 to 40 minutes, during which there will be no movements.
The number of movements increases until 32 weeks gestation, and remain the same until delivery, although the type may alter nearer to the estimated date of delivery.
Foetal movements are less noticeable if one is busy, and during labour.
There is no specific number of movements that is considered normal. Every mother should be aware of their child’s individual pattern of movements.
If you’re unsure whether there is a reduction, all that is needed is to lie on the left side and concentrate on the movements for the next two hours. If there are less than 10 or more separate movements during this time, medical attention should be sought. This should be done immediately if the pregnancy is more than 28 weeks.
Foetal heart rate
The foetal heart rate (FHR) is monitored during pregnancy and labour by the midwife, who will ask the attending doctor to check mother and foetus, if she has any concerns. It is measured either at regular intervals (intermittent), or continuously during labour. The former is the usual mode of monitoring when there are no pregnancy complications.
In addition to intermittent monitoring, the FHR will also be checked before and after vaginal examinations, or when the membranes rupture.
There are situations in which continuous FHR monitoring will be advised. This would include maternal or foetal health, labour reasons, or abnormal FHR on intermittent monitoring, ie less than 110, or more than 160, beats per minute, or slowing of the heart rate (deceleration) after a contraction. The maternal reasons include raised blood pressure, diabetes, infection, and heart or kidney problems. The foetal reasons include pregnancy past 42 weeks, foetus that is small for date or premature, attempted vaginal breech delivery, and multiple pregnancies.
Continuous monitoring is also advised when the mother’s labour is augmented or induced, there is vaginal bleeding prior to or during labour, significant meconium staining of the liquor, maternal fever, and if the mother had a previous Caesarean section, or has epidural or spinal analgesia. Some mothers who have no pregnancy or labour problems may also request continuous monitoring.
There are two graphs on the cardiotocograph (CTG) – the upper graph records the FHR in beats per minute, and the lower graph, the maternal contractions in millimetre mercury.
The normal FHR is between 120 and 160 beats per minute. The constant up and down fluctuations of five to 25 beats from the baseline (variability) reflects a healthy foetus. An increase above the baseline with foetal movement is reassuring.
The FHR may decrease slightly during a contraction (deceleration). This is normal, provided the FHR recovers rapidly once the contraction stops.
Decelerations are described as early or late, depending on its occurrence in relation to uterine contractions.
Change in the baseline, especially if prolonged, has loss of or increase in variability, and late or prolonged decelerations are not reassuring.
False positive CTGs (ie changes indicative of a problem when there is none) are common. They are associated with increased assisted deliveries with ventouse or forceps, and Caesarean sections. This is the reason why the term non-reassuring foetal status is preferred.
Meconium is produced by the foetal gut, and comprises materials ingested by the foetus in the uterus, ie intestinal epithelial cells, lanugo, mucous, amniotic fluid, bile, and water. It is the earliest faeces of an infant, and is dark green, almost odourless, viscous, and sticky like tar. It is usually stored in the foetal gut until after birth, but sometimes, it is expelled into the amniotic fluid before or during labour, and delivery.
It is completely passed after the first few days of life, with the stools becoming yellow.
Amniotic fluid is usually clear. But if it is of various shades of green or brown, it is an indicator that the foetus has passed meconium. Meconium may be a sign that the foetus has problems, although it is common to find meconium in the amniotic fluid of women past their estimated date of delivery.
Thick meconium is of concern as it may get into the foetal airways and cause meconium aspiration syndrome (MAS). Meconium irritates the lungs, causes infection of the airways and may block it, thereby leading to breathing difficulties at birth.
Foetal blood sampling
Foetal blood sampling (FBS) assists in clarifying the significance of abnormal FHR changes and confirms if the foetus is short of oxygen (hypoxic). It involves taking a few drops of blood from the foetal scalp through the vagina.
It is checked for the levels of oxygen, carbon dioxide and pH. This will provide information about how the foetus is coping with the stress of labour.
FBS is not carried out sometimes because of maternal infection or when such facilities are not available in the hospital.
Dealing with non-reassuring foetal status
If the FBS results are within normal range, labour will usually be allowed to proceed. The FBS may be repeated if they are borderline normal.
If there are concerns about the results, the therapeutic measures taken will include giving the mother oxygen by face mask; turning her to her left to reduce uterine pressure on a large vein in the back (vena cava), thereby improving the blood flow back to the heart and consequent blood flow to the placenta and foetus; temporarily stopping medicines that increase uterine contractions; and increasing fluid intake through an intravenous drip.
If the above measures do not lead to an improvement in the FHR, delivery of the foetus will be expedited. Depending on the stage of labour and the cervical dilatation, assisted vaginal delivery with a forceps or ventouse, or emergency Caesarean section will be carried out.
As the patient may be alarmed at the turn of events, the obstetrician or midwife will provide an explanation and the reasons for the measures being taken.
■ Dr Milton Lum is a member of the board of Medical Defence Malaysia. This article is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organisation the writer is associated with. For further information, e-mail firstname.lastname@example.org. The information provided is for educational and communication purposes only and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this column. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.