This ultrasound scan is one of the most important tests of your pregnancy. It can be done from 11 to 14 weeks (baby’s length CRL 45– 84 mm). It is usually performed from the tummy, although, in some cases, it might be necessary to do it through the vagina.
What are the purposes of the 11- 14 weeks scan?
- To calculate precisely the gestational age
This is of great importance to women that do not know or are unsure about the exact date of their last period or if their periods are irregular, conceived while breastfeeding, or conceived shortly after coming off their contraceptive method. By measuring the baby’s lenght from head to the tip of the spine (crown- rump length, CRL) we can calculate, with great accuracy, the exact gestational week and subsequently inform you about the estimated due date.
- To diagnose multiple pregnancy
Approximately 2% of natural and up to 10% of assisted reproduction conceptions end up in multiple (twins, triplets etc) pregnancies. The scan can help distinguishing the presence of more than one babies. Additionally, it can clarify if in twin pregnancies there are two separate or if the babies share one, common, placenta. In the latter case (monochorionic pregnancy) complications are more common and follow up has to be closer.
- To exclude a miscarriage
Unfortunately, in about 3% of the cases, when a scan is done we discover that the pregnancy is not developing properly and that a miscarriage happened even a few weeks before. That is possible even if no symptoms re present. In this case, we will explain to you in details all of your options and what are the next steps that need to be done.
- To diagnose major fetal abnormalities
In about 1% of pregnancies, the baby has some structural abnormality which may be visible even from this stage of pregnancy. If such a congenital anomaly is detected we will discuss the findings with you. We might need to repeat the scan to confirm findings or we can perform additional testing to find the exact cause of the abnormality (CVS, amniocentesis).
- To calculate the probability of Down syndrome (Trisomy 21)
Each woman can have an idividualised estimation of the probability her baby has Down syndrome. The probability is calculated by taking into account the maternal age, measuring two hormones in the mother’s blood (free β- hCG and PAPP- A) and ultrasound markers like the nuchal translucency, the nasal bone, the blood flow through the tricuspid valve into the heart and the ductus venosus of the baby. Parents will be offered detailed counseling about the meaning of the result and the available options for further testing, if indicated.
- Preterm birth probability estimation
The probabilty preterm birth (delivery before 37 weeks) happens can be estimated by measuring the cervical length and taking into account the gynecological and obstetric history. This scan is suggested to all pregnant women but it can be even more important in high risk cases for preterm birth, like multiple pregnancies, history of preterm birth in the past, congenital uterine abnormalities, history of cervical procedures (cone biopsy) and the mother’s connective tissue/ collagene diseases. Measuring cervical length is done transvaginally and is absolutely safe for both the mother and the baby.
- Intrauterine growth restriction and preeclampsia probability estimation
This is an optional test that includes the combination of the uterine arteries blood flow evaluation and the levels of biochemical markers in the maternal blood, namely PAPP- A and PLGF. This way, we can calculate the probability of a baby being growth restricted during fetal life and the mother to develop preeclampsia, a pregnancy complication. This test is particularly useful for women with a history of a growth restricted fetus in a previous pregnancy, preeclampsia, diabetes mellitus or if are heavy smokers. Based on the results obtained we can discuss about available options, including pharmaceutical treatment needed, or schedule more frequent appointments.