The number of scans each woman has during her multiple pregnancy will vary greatly depending on the type of twins or multiples she is carrying. For example a mother carrying monochorionic monoamniotic twins will undoubtedly have more scans than a mother carrying dichorionic diamniotic twins as the former carries more risk of complications. Previous medical history of the mother will also determine the need for further scans. Therefore the timing and frequency of scans is determined case by case. The routine scans in NZ are around 11-13 weeks (Nuchal translucency scan) and at 18-20 weeks (this scan is to check the anatomy of the babies and the position of the placenta). For multiple births you would expect to have additional scans to check the growth of your babies.

What they measure in dating and growth scans: 

The Crown-rump length (CRL)

This measurement is only taken weeks 7 to 13 to give an accurate estimation of the gestational age. 

The Biparietal diameter (BPD)

This is the diameter between the 2 sides of the head. This measurement is not taken until after 13 weeks

The Femur length (FL)

The femur is the longest bone in the body so by measuring it we get an idea of how the foetus is growing lengthwise

The Abdominal circumference (AC)

Toward the end of the pregnancy this is the most valuable measurement as it gives an idea of size and weight. 

The data collected at each scan is put through a computer programme which calculates an estimated weight and gestational age. These results are recorded on a growth chart which shows average growth for a singleton foetus. A series of these scans will give your LMC a good idea of how your baby is developing and whether there is any cause for concern.

Remember that people take the measurements so there can be variation between sonographers. It can be helpful to try to get all your scans done by the same clinic so that there is some consistency in your results.

Although pregnancy treatment in New Zealand is meant to be free you CAN be charged for scans. If you are carrying multiples it may be a good idea to check the charges in a few clinics in your area.