The third ultrasound during pregnancy: when, at what time?


  • Conclusion
  • With the advent of ultrasound, the woman still at the stage of pregnancy can learn about the health of your baby and can even determine its gender, height and weight. If successful pregnancy ultrasound is performed three times: at the twelfth, twenty-second and thirty-second week. By the time the third study, the child has already formed in the womb and a diagnosis of his condition is important to determine the tactics of further pregnancy and childbirth.

    The purpose of the ultrasound in the third trimester of pregnancy

    Held for a period of thirty-two weeks and included in the list of compulsory examinations of a pregnant woman before entering the hospital. As a rule, during the first and second ultrasound already revealed a large part of the anomalies, so a third survey aimed at identifying pathology that is visible only in the later stages of child development.

    Begin to do the screening with an assessment of the movements and the heartbeat of the fetus. If multiple pregnancy, examination of each fruit, make and describe separately. The importance of fetal presentation (position it in the womb of a relatively small pelvis of the mother).

    The most favorable presentation – parent, when child is head to the pelvis of the mother, in this case, natural childbirth involve least complications.

    Also there is breech presentation, when the pelvis of the mother the child is legs or booty. In this case, natural childbirth is possible in half of the cases, it has more complications and requires additional control of the obstetrician at the hospital.

    When the transverse position of fetus delivery is only possible with a caesarean section.

    An estimate of the heartbeat do the Doppler, which allows us to estimate not only the rate and rhythm of contractions, but also the correct development of the heart chambers, absence of congenital malformations. Then carry out the screening of organs and systems, their development and abnormalities. Do measurements of the baby.

    Table 1. Normal values of the main dimensions of the foetus at the thirty-second week of development.

    The estimated parameter

    The normal value for 32 weeks (mm)

    Biparietal head size – distance from the outer surface of the right bone to the inner surface of the left

    72 – 89

    Fronto-occipital size – distance between the outer surfaces of the frontal and occipital bones

    95 – 113

    The circumference of the head (measured on the outer loop)

    283 – 325

    Abdominal circumference on the outer contour

    258 – 314

    Length of leg bones


    56 — 66

    51 — 61


    52 — 60


    45 — 53

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    If the measured values are significantly behind normal, talking about intrauterine growth retardation. However, the performance may slightly lag from the norm by reason of hereditary characteristics, for example, if the child’s parents of low growth.

    Intrauterine growth restriction (IUGR) is symmetric when the body dimensions symmetrically reduced and asymmetric in the development lags behind what is only one part of the body, for example, in the normal development of the brain underdeveloped abdominal or thoracic cavity.

    IUGR is divided into three degrees of severity, depending on how far behind the size:

    • 1 degree: no more than two weeks (mild)
    • 2 degree: from two to four weeks (medium)
    • 3 degree: more than four weeks (severe degree) usually leads to the death of the fetus.

    The presence of anomalies and deviations in development

    This section devotes a lot of time during the ultrasound on the twenty-second week. But during the screening in the third trimester, the physician carefully examines the organs of the child for any abnormalities and defects, some of them are visible only in this trimester. Revealing some deviations from the norm during this period can cause a drastic change of tactics of childbirth. So in the presence of hydrocephalus or umbilical hernia conducting natural births can cause a number of complications for the baby and for the mother, and is an indication for cesarean section.

    Evaluation of provisional organs

    This section is also very important before delivery, as is also one of the main factors determining which method is preferable.

    Placenta (children’s place)

    Her condition is important for a child in the womb because the placenta is the life support of a growing organism (nutrition, respiration, metabolism, etc.).

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    During ultrasound screening in the third trimester make inspection of the placenta and its compliance with the maturity term of the pregnancy. Intrauterine growth restriction of the baby in the third trimester of pregnancy in most cases is associated with disruption of the placenta.

    Is set to the location of child seats in the uterus. If the location of the placenta falls to the mouth of the cervix, If there is partial, and the more complete placenta previa (the location of the placenta falls to the mouth of the cervix), increases the threat of premature interruption of pregnancy, when breech presentation is a complete natural childbirth impossible.

    Amniotic fluid

    Assessment is done through calculation of the index of amniotic fluid, which is done by a specialist. Normal values range from two to eight inches, when the deviation in the smaller side need to talk about water scarcity, large – polyhydramnios.

    The umbilical cord

    This temporary organ that connects the mother and child through three vessels: two arteries and one vein. In some cases it is only two vessels in the umbilical cord (one artery and Vienna), in this case you need to carry out increased monitoring of the condition of the fetus.

    Also, during the ultrasound screening is the detection of entanglement of umbilical cord around the baby’s neck. In severe cases (double tight entanglement) required a cesarean section to avoid fetal asphyxia during labor.

    A full assessment of the condition of the fetus in the third trimester is done through the assessment of biophysical parameters. Screening is carried out in points on a scale.

    Table No. 2. Scale observations of biophysical parameters.

    Settings The time of observation   Score (points)  
    rapid heartbeats 1 2
    rapid heartbeats 20 minutes less than 2 accelerate 2 – 4 acceleration 5 accelerate
    respiratory motion 30 minutes 1 episode shorter than 30 seconds or no at least 1 episode of 30 to 60 seconds at least 1 episode is equal to or greater than 60 seconds
    generalized movement 30 minutes lack of movement 1 -2 at least three
    muscle tone 30 minutes the fruit is in extension position at least 1 episode of extension movement of the back or limb with return to flexion of the former position at least 1 episode of extension movement of the back and limbs and return to the previous flexion position
    the vertical depth of the free land of amniotic fluid (cm) less than 1 1 – 2 2 and more
    maturity of the placenta (degree) 3 location inaccessible to examination 0, 1, 2
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    The results (in points):

    • 8 – 12 – normal development of the child
    • 6 – 7 – the threat of complications
    • 5 and less – intrauterine fetal hypoxia

    If during a routine ultrasound screening revealed abnormalities of child development, developmental delay or pathological changes of the placenta can be assigned to one or even several studies with a certain interval to control the dynamics and evaluation of results of treatment (if it was) before birth. Before delivery can be made for another screening, if during the preceding determined suffocation by an umbilical cord or breech presentation of the fetus.


    Expectant mothers are very concerned about the issue: don’t hurt baby ultrasound scans, and sometimes even such doubts are cause for rejection of the study. Currently, long-term experience of applying this type of screening among different categories of people, including pregnant women and children, confirmed its absolute safety even with frequent running. Abandoning the diagnosis, the woman risks the health of your baby, often unnecessarily, because many abnormalities are successfully treated at the stage of pregnancy, and the awareness of physicians about the status of provisory organs before admission to the hospital, to avoid complications during childbirth, which often can even become the cause of death or disability of the child.