Q I am 30 years old and pregnant for the first time. I had spotting on and off in my second month. I am now five months' pregnant and had a foetal anomaly scan recently.

My gynaecologist told me that my placenta is low and I may not be able to deliver normally. I had another episode of bleeding a week ago and had to be admitted to hospital for observation.

Is this placenta previa? What are the causes? I am very anxious and worried whether this will affect the baby. When can I deliver the baby?

A The placenta is a circular, flat organ that begins to form soon after conception. It provides oxygen and nutrients to, and removes waste products from, the growing baby. It performs these functions by attaching itself to the wall of the womb (uterus) and the baby's umbilical cord, thus forming a vital connection between mother and baby.

Most of the time, the placenta is located in the upper part of the uterus. In about 5 to 10 per cent of pregnancies, however, it attaches itself to the lower part. As a result, the neck of the womb (cervix) may be blocked partially or completely. This is known as placenta previa.

It can cause profuse vaginal bleeding when the cervix begins to open in preparation for labour. This can pose problems for both mother and child.

Bleeding associated with placenta previa usually occurs near the end of the second trimester or the beginning of the third. However, as in your case, some women may have light bleeding or spotting during the first trimester or early second trimester. It is usually painless and can occur without warning. The amount of bleeding may range from light to heavy. The bleeding usually stops, but always recurs days or weeks later.

The cause of placenta previa is not known. There are some risk factors which are absent in your case. These include previous uterine surgery, such as removal of a fibroid; overzealous curettage (D and C) to scrape the uterine lining, as in an abortion; a large placenta, as in a multiple pregnancy (twins or triplets); a previous Caesarean section; later pregnancy (age 35 and above), and smoking.

Although your second trimester ultrasound shows that you have a low placenta, it may not mean that it has blocked the cervix. As your pregnancy progresses, the placenta may 'migrate' further from your cervix and no longer pose a problem. It should be noted that the placenta does not actually move. It may simply end up further away from the cervix as the uterus expands.

A follow-up ultrasound in your third trimester should be done to confirm the location of the placenta. If it is blocking the cervix, you will be monitored carefully and watched for vaginal bleeding.

A Caesarean section is the only option for delivery in this case.

As to when to deliver your baby, it depends on the following factors: severity and amount of vaginal bleeding; whether the bleeding has stopped; whether the mother is in the medical state of shock; whether the mother is in established labour, and the gestational age of the baby and its state of health.

If bleeding is severe and the mother's health compromised, the baby should be delivered immediately, even if premature. A blood transfusion may be necessary.

Otherwise, a policy of 'masterly inactivity' - wait and see - is usually followed and a Caesarean section planned for when the baby has a good chance of survival.

DR PETER CHEW, CONSULTANT OBSTETRICIAN AND GYNAECOLOGIST, GLENEAGLES HOSPITAL