Prenatal Ultrasound Examination Tips

Pregnancy is a happy and long process for every pregnant mother. It is well known that pregnant mothers need to do various examinations during pregnancy, one of the important examinations is the prenatal ultrasound examination of the fetus. However, in real life, for many new mothers, these pregnant mothers do not know when these prenatal ultrasound examinations should be done. So today, let us start from the perspective of prenatal ultrasound examination of the fetus and develop a clear prenatal ultrasound examination strategy for new mothers.

1. What is prenatal ultrasound?

The so-called prenatal ultrasound examination of the fetus actually refers to the application of ultrasound technology to perform corresponding imaging examinations on pregnant mothers and fetuses to provide corresponding references for the doctor's diagnosis. However, it is worth noting that this prenatal ultrasound examination cannot directly represent the pathological diagnosis or clinical diagnosis of the pregnant woman. Because the clinical diagnosis during pregnancy covers a lot of content, such as the pregnant woman's medical history, physical signs, genetic counseling, medical imaging, biochemical immunology, cytogenetics and molecular genetics, so prenatal ultrasound examination can only provide corresponding references for clinical diagnosis.

2. What are the main contents of prenatal ultrasound examination?

For new mothers, the ultrasound examinations required at different stages of pregnancy are different, and the purpose of the examinations is also different. Prenatal ultrasound examinations are mainly to check the specific conditions of the fetus at different stages of pregnancy, such as the examination and strategy of the fetal structure and fetal appendages, in order to assess whether there are any abnormalities in the growth and development of the fetus in the uterus. According to the period of pregnancy, there are mainly the following types of prenatal ultrasound examinations of the fetus:

2.1 Ultrasound examination in early pregnancy

Early pregnancy mainly refers to the period of pregnancy that does not exceed 14 weeks. During this period, the ultrasound examinations that pregnant mothers need to undergo include conventional ultrasound examinations in early pregnancy and four-dimensional NT examinations.

(1) Conventional ultrasound examination in early pregnancy

The so-called ordinary ultrasound examination in early pregnancy is actually an ultrasound examination performed within 6-8 weeks of the pregnant mother's menstruation. There are many purposes for this examination. The ultrasound examination during this period needs to check the implantation position of the embryo in the pregnant mother's body to determine whether it is an intrauterine pregnancy or an ectopic pregnancy. If the pregnant mother has a history of cesarean section, it is also necessary to check the relationship between the implantation position of the embryo and the cesarean section scar. In addition, the examination during this period needs to determine the number of embryos in the pregnant mother's uterus, determine whether the pregnancy is twins, single or multiple, and determine whether the fetus has a fetal heart. At the same time, the ultrasound examination in early pregnancy also needs to judge the size of the embryo to see if the size of the embryo is consistent with the gestational age. If the pregnant mother has irregular menstruation or cannot effectively remember the time of her last menstrual period, the gestational age of the pregnant mother can also be calculated based on the size of the fetal bud indicated by the ultrasound examination. In addition, the uterus and appendages of the pregnant mother need to be examined in the early ultrasound examination. If the pregnant mother has vaginal bleeding or abdominal pain in the early pregnancy, an ultrasound reexamination is usually required.

(2) Four-dimensional NT examination

Generally, the four-dimensional NT examination needs to be performed between 11 weeks and 13 weeks + 6 days of pregnancy. For pregnant mothers, it is very important to perform a four-dimensional NT ultrasound examination during this period, because the NT ultrasound examination can effectively measure the thickness of the fetal nuchal translucency layer (NT) during this period. Normally, the normal value of NT is ≤2.5mm. If the fetal NT value is thickened during the NT ultrasound examination, the fetus may have chromosomal abnormalities. In addition, the NT ultrasound examination can also recalculate the gestational age of the pregnant mother based on the head-butt diameter of the fetus to ensure the accuracy of the gestational age. At the same time, this ultrasound examination can also observe the placenta and amniotic fluid of the fetus, and can detect some serious cranial malformations in early pregnancy, so the NT ultrasound examination is also a preliminary fetal morphological examination. If the fetus is a twin, then the chorionicity of the twins needs to be determined again. In addition to the above examination contents, this ultrasound examination can also examine the space-occupying area of ​​the pregnant mother's uterus and adnexa.

2.2 Ultrasound examination during the second trimester

The time of mid-pregnancy is between 14 and 28 weeks of gestational age. During this period, the ultrasound examination that pregnant mothers need to undergo is a major fetal malformation examination. The appropriate gestational age for this major fetal malformation examination is between 20 weeks and 24 weeks + 6. Because the structural development of the fetus is relatively complete during this period, and the size of the fetus and the amount of amniotic fluid are relatively moderate, it is very suitable for ultrasonic structural malformation screening. During this period, pregnant mothers do not need to fast when conducting major fetal malformation examinations, and pregnant mothers can also have a proper diet before the examination to increase fetal movement and promote the smooth progress of the examination. According to the "Guidelines for Ultrasound Prenatal Screening" issued in 2022, major fetal malformation screening can be performed during the 20-24 weeks of pregnancy. There are 9 main types of severe fetal structural malformations that can be screened out, such as fetuses with anencephaly, lobar holoprosencephaly, or severe open spina bifida with myelomeningocele, which can be screened out in this ultrasound examination. At the same time, during this ultrasound examination, the doctor will also measure the fetal biparietal diameter, head circumference, abdominal circumference, and femur length, and effectively screen the development of fetal organs to avoid structural abnormalities in the head, face, spine, heart, limbs, etc. Therefore, after a major fetal malformation screening in the second trimester, the doctor can conduct a multi-dimensional assessment of the growth and development of the fetus by observing and measuring the fetal structure. At the same time, based on these evaluation results, it is also possible to understand some hidden abnormalities that may exist in the fetus by combining other fetal examinations.

2.3 Ultrasound examination in late pregnancy

The so-called late pregnancy actually refers to the situation where the pregnant mother's gestational age exceeds 28 weeks. During this period, the prenatal ultrasound examinations that pregnant mothers need to undergo include 28-week ultrasound examinations and ordinary ultrasound examinations in the late pregnancy.

(1) Ultrasound examination at 28 weeks of pregnancy

The ultrasound examination performed at 28 weeks of pregnancy needs to check the growth and development of the fetus, such as the placenta, amniotic fluid depth, and umbilical cord condition of the fetus. In addition, during the examination, it is necessary to observe the structure of the fetus in a suitable fetal position, and at the same time, do another screening for missing and filling deficiencies in the fetal system structure malformations to rule out common malformations in late pregnancy, such as limb shortening, hydrocephalus or hydronephrosis, and gastrointestinal atresia. Moreover, this screening can re-screen organs that were not seen in the mid-pregnancy examination. However, it is worth noting that due to factors such as the pregnant mother's abdominal wall and the fetal position, this examination cannot be comprehensive and detailed, so this examination is only a screening for malformations to fill deficiencies.

(2) Conventional ultrasound examination in late pregnancy

During a routine ultrasound examination in the third trimester, the doctor will assess the growth and development of the fetus, and observe the fetal position, amniotic fluid depth, and the condition of the placenta and umbilical cord. However, it should be noted that the assessment of fetal weight during ultrasound examination is only an estimate and is not completely accurate.

**Summary:** Pregnancy is a happy process of nurturing a new life. In order to ensure the health of the fetus and the normality of pregnancy, pregnant mothers need to undergo regular prenatal examinations during pregnancy. In prenatal examinations, ultrasound examination is a very important examination item, which enables pregnant mothers to understand the condition of the fetus at different stages. Therefore, inexperienced novice mothers can refer to the above examination guide to prepare for the healthy birth of the baby.