Hi I am 24 years old, I had an abortion 2 years ago.. And now I am pregnant again.. If I go by my lmp I am 16 weeks, going by my first ultrasound I am 17 weeks..

What I want to know should I be worried that my cervical length is 4.Cm and if I am I at risk for preterm labor or cervical issues.

Also should I go by my lmp or ultrasound scan to determine how many weeks I am..

Two dates are seen in pregnancy. Gestational age is taken from the first day of your last period. This is what is usually used for dating a pregnancy as most women do not know exactly when conception occurred. Fertilisation age is when conception actually occurs... this is not usually known unless medical assistance was used to become pregnant. Your doctor or midwife is likely now going by the dates you have from ultrasound results. It is common practice to move due dates, and weeks of pregnancy, up or back a bit from what is seen on the ultrasound.

Although not an exact science, it is thought to probably be a bit closer. However, the differences in dates is partly why you have a window of time at the end of pregnancy that is considered "term" for giving birth in.

Ultrasound in early to mid-pregnancy usually gives the more accurate dates as babies tend to follow a fairly uniform course of development in early pregnancy. Ultrasound later in pregnancy becomes less accurate as growth patterns can be more individual.

A cervical length of 4 cm is right on target. Enjoy your pregnancy!