In the second trimester, a pregnant woman is assigned a repeated screening, confirming or refuting the data obtained in the first comprehensive study. This period is most suitable for the diagnosis of hormonal levels of the fetus. The data obtained make it possible to assess its development.
If the expectant mother has to wait for a consultation of the attending physician for several days, she will certainly be interested in whether the results of the perinatal screening are normal in advance. It should be remembered that the doctor always judges the pathology only by the totality of the indicators of fetometry, and almost never takes anyone value into account.
Each child is individual even before birth. And if the future mother has really serious reasons for concern, then the ultrasound clinic will inform her about this immediately. Nevertheless, we will talk about the main indicators of the second screening and their normal values.
Body length and fetal weight
At the beginning of the second trimester, the embryo is growing very actively, and it is difficult to judge the standards. On average, the length of the fetus grows from 10 to 16 cm between the sixteenth and twentieth weeks of pregnancy. It is important to consider not an absolute indicator in centimeters, but an increase in growth by weeks. If the specialist is alert, the pregnant woman will be offered a second study after a week or two.
The fetal weight by ultrasound can only be determined using special formulas so that this value can be very inaccurate depending on the device, the doctor, and the posture of the baby in the womb. Weighing about 300 grams by the 20th week, all the organs of the baby are fully formed, and from 22 weeks or about 450 grams, a prematurely born baby can survive. It seems unbelievable!
The circumference of the abdomen and head
As well as the growth of the child, these important values vary over a wide range and must strictly correspond to the gestational age. There are frequent cases when the “developmental delay” in practice turned out to be an incorrectly diagnosed gestational age. However, the widespread introduction of ultrasound diagnostics in the early stages has reduced the number of such errors.
Biparietal (BPR) and Frontooccipital Foetal head size
It is not surprising that the level 2 ultrasound of pathologies during pregnancy is based on head measurements in 3 projections. It is unlikely that at least one human organ is comparable in complexity and importance to the brain. Deviations from reference values may indicate the formation of severe fetal malformations, such as anencephaly or dropsy of the brain. But as a rule, such diseases are judged by several repeated ultrasounds.
Bone length: lower leg, femur, humerus, and forearm
Some deviation from the norms indicated in the table for the weeks of pregnancy is permissible and can be determined by individual characteristics. The doctor will be warned by a sharp shortening of the entire limb or a different length of arms or legs in one child.