1. You just feel that you are carrying more than one baby. Some mothers of twins (or higher order multiples) say that they knew right from the start that they were carrying more than one baby.

2. You experience more nausea and/or morning sickness. If you are having more than one baby, you may have an elevated hCG level (hCG is a pregnancy related hormone). This hormone is the one associated with morning sickness.

3. Other typical pregnancy symptoms may be exaggerated. Many women -- but not all -- who are pregnant with twins have more intense pregnancy symptoms, probably related to the extra hormones circulating through their system. You may find that your breasts are extremely tender, you have to urinate frequently, you are hungry all the time and you are always very tired.

4. A higher than average weight gain in the first 16 weeks may be your first clue that you're carrying more than one baby. Good weight gain in early twin pregnancy is associated with a favourable outcome.

With each additional fetus a woman carries, the range of weight gain will increase. For example, a woman who starts a pregnancy in a healthy weight range might expect her weight gain to be as follows:

One fetus, 11 kg (24 lb) to 16 kg (35 lb)

Twins, 16 kg (35 lb) to 20 kg (44 lb)

Triplets, 20 kg (44 lb) to 23 kg (51 lb)

Quads, 23 kg (51 lb) to 25 kg (55 lb)

5. Your uterus seems large for gestational age. If your last menstrual period indicates an eight-week gestation, your uterus may feel more like 10 to 12 weeks to your obstetrician. This may prompt a request for an ultrasound examination.

6. You are told that you have elevated levels of AFP. AFP is one of the chemicals tested to screen for Down’s syndrome and spina bifida abnormalities. AFP levels are higher in twin pregnancies.

7. Your health care provider hears two fetal heartbeats. Two separate heartbeats can be distinguishable with a Doppler in your care provider's office from around 18 weeks. At around 28 weeks, it may be possible to differentiate two fetal heads and multiple small parts when doing an abdominal exam.

8. You have a positive ultrasound. If you believe you are pregnant with twins, an ultrasound can be performed quite early in pregnancy. With a skilled ultrasonographer, two gestational sacs, two embryos and two distinct fetal heartbeats can be seen six weeks after the first day of the last menstrual period. Many twins have been diagnosed as early as five weeks -- when you're just one week late for your menstrual period.

9. In later pregnancy, you may experience difficulty catching your breath, swelling (oedema) of the hands and legs, an unusual rate of weight gain and abdominal enlargement and excessive fetal movement. Anaemia or low iron (decreased haemoglobin) is also common with twin and multiple pregnancies.

10. There is considerable disagreement among medical professionals as to whether a woman carrying twins is more likely to feel movement earlier. But many mothers do claim that those early flutters and flips were their first clue that they might be having more than one.