- Why and How is Ultrasound Used in Pregnancy
- When to Do Ultrasound
- Peculiarities of 3D and 4D Imaging
- Is it Harmful Ultrasound
How Many Ultrasounds do You Get During Pregnancy
During pregnancy, every woman is looking forward to the next ultrasound: it is so cool to see on the screen your baby sucking a finger, yawning or sweetly sleeping. However, ultrasound allows not only see your unborn baby, but also safely monitors his development from the beginning of the pregnancy and assesses the mother’s state of health.
Why and How is Ultrasound Used in Pregnancy
All pregnant women make an ultrasound scan to:
- confirm the pregnancy;
- assess the fetal state and detect abnormalities of the development, if there are any;
- measure the baby;
- study the location and structure of the placenta and the umbilical cord;
- estimate the amount of amniotic fluid;
- assess the blood flow in the uterus, placenta and blood vessels;
- assess the state of the ovaries, uterine walls and cervix.
There are two types of ultrasound scans: transabdominal (through the front wall of the abdomen) and transvaginal (a special transducer is inserted vaginally), it is believed that the second type of scanning is more reliable. Before the study, the doctor applies a thin layer of a special gel that contributes to the good contact of the ultrasound waves with the abdomen area.
When to Do Ultrasound
Women with the normal course of pregnancy are offered to make ultrasound scans in the following terms:
- in the first trimester of pregnancy between 11 and 13 weeks (+ 6 days);
- in the second trimester – between 20 and 24 weeks;
- in the third trimester – between 30 and 32 weeks.
However, if you need more information about the state of the baby, the number of scans can be increased, but they are not performed only to allow you to see your baby one more time, they are made strictly on the prescription of your doctor.
First Trimester Ultrasound
Quite often, in the first trimester ultrasound scans are made twice: in the early pregnancy and between 11 and 13 weeks.
In the early pregnancy, doctors:
- exclude ectopic pregnancy;
- estimate the number and size of the ovum (inner diameter and crown-rump length of the fetus);
- determine the duration of pregnancy;
- evaluate the heartbeat in the embryo and its motor activity;
- study the amnion, the chorion, the umbilical cord and the yolk sac;
- detect abnormalities of the reproductive organs (uterine structure abnormalities, ovaries formation, fibroids, and intrauterine abnormalities), if there are any;
- diagnosis pregnancy complications (threat of a miscarriage, a beginning or a complete abortion, molar pregnancy).
As a rule, starting with the third week after the conception it is possible to detect the ovum in the uterine; within 4-5 weeks, the embryo is already visible. At the same term doctors can estimate the fetal heartbeat, and the assessment of motor activity is carried out starting with 7-8 weeks of pregnancy.
The yolk sac is about 2-6 mm; it should disappear by the 12th week. Lack of a yolk sac or its early obliteration are bad signs.
In addition to the mentioned indicators, between 11 and 14 weeks are detected gross malformations (anencephaly, skeletal anomalies, etc.), as well as markers of chromosomal abnormalities (Down’s, Turner, Edwards’ syndromes, etc.). The results of this ultrasound scan along with the biochemical screening in the first trimester allow to identify up to 95 % of children with such abnormalities.
Second Trimester Ultrasound
During this period, ultrasound is carried out between 20 and 24 weeks. Some clinics offer an additional scan between 16 and 18 weeks (it is included into the so-called "triple test" — the second biochemical screening).
At this term of pregnancy, ultrasound allows to define:
- dynamics of growth (the circumference of the head and the abdominal, the femoral length) and the weight of the fetus;
- intrauterine growth abnormalities (ventriculomegaly, pyelectasis, abnormal skull and cerebellum shape, etc.);
- location, thickness and structure of the placenta;
- the amount of amniotic fluid.
A Doppler ultrasound is a compulsory test that is used to estimate the blood flow between the mother, placenta and the fetus and detect hypoxia, if it is present. It is also used to check the placenta’s location: in case of the placental presentation that may cause hemorrhage or abruption, the woman is prescribed to make ultrasound scans every four weeks.
The final diagnosis is made at the end of pregnancy. Doctors also measure the length of the cervical canal, the cervix, and assess the risk of preterm birth. They can also determine the baby’s sex with great probability.
Third Trimester Ultrasound
At this term, ultrasound allows to identify:
- delay and not previously detected abnormalities of the fetal growth;
- violations of the functional status of the fetus and the blood flow;
- the final location of the placenta and its maturity;
- changes in postoperative scars on the uterus.
By this time, the fetus usually takes the position to be born, therefore, doctors also define its lying (head or bottom down), the umbilical cord entanglement, forecast his weight at birth and specify delivery dates.
The amount of amniotic fluid is also important: hypamnions or hydroamniosis may be signs of an infection or a malformation of the fetus. A biophysical profile is used to assess fetal well-being, it is a comprehensive analysis of the data obtained with ultrasound and cardiographic studies.
Peculiarities of 3D and 4D Imaging
Three-and four-dimensional ultrasound scans are new techniques that allow you to see the three-dimensional image of your baby. 3D-study can be used to confirm certain developmental defects (e.g., a cleft palate or a harelip) and 4D-study shows the baby in motion. The main purpose of such ultrasound formats is the aesthetic pleasure of the parents, usually, the two dimensional ultrasound is enough to detect any malformations.
Is it Harmful Ultrasound
There is still no definite answer to this question. Over the years, such studies have not revealed that ultrasound may affect the fetus; however, periodically scholars make such hypotheses. That is why experts advise to undergo ultrasound scans in due terms and do not make scans, if there are no specific indications, at least before 10-12 weeks.