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Ultrasound and Scans: A Peek Through the Womb
PHOTO BY @esp2k/iStock
  • Expectant parents cannot deny the exhilarating experience of viewing their unborn child through ultrasound. But before you scurry for a scan, one has to be aware of the fact that it is “unrealistic and unreasonable to expect detection of all fetal anomalies even with the most expert and thorough scanning. (American College of Obstetrics and Gynecology).

    The Unheard Sound

    “Ultra” means ‘extremely’ while “Sound” per se is made up of vibrations that travel through air, water or some other media like body tissues to reach a certain threshold and be heard by the human ears.

    Thus, the compound word ultrasound is synonymous to ‘hyper-phonography” which is not audible since they are EXTREMELY high frequency waves traveling above the limit of human hearing.

    Who performs the scan?

    The following are the medical specialists equipped with the expertise to do the much anticipated scan:
    •    From the mother Society of Obstetrics and Gynecology, Fellows of 2 subspecialties in the field of Sonology and Perinatology are board certified physicians who are highly trained to scan and explain the findings.

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    •    Radiologists on one hand are physicians with specialized training in interpreting images from radiographs, magnetic resonance, tomography and ultrasound as well.

    How safe is the procedure?

    Except for isolated cases of hypersensitivity to latex material from the condom used during transvaginal scan and mild allergic rash for mothers with sensitive skin on application of utrasonic gel, there are hardly any risks involved.

    Presently, no definite scientific data is out to prove any damaging effect on the embryos exposed in utero to ultrasound waves for over a half century of use. There is no reported risk such as ionizing radiations as in X-rays, likewise long term studies have not linked ultrasound to problems in neurological development and future school performance of the child.

    The First Trimester Scan (FTS) - 5 to 13 weeks

    A positive pregnancy test does not always equate to a live baby!

    Picture a couple elated upon seeing the double lines in a pregnancy test, only to find out through early ultrasound the following possible findings:

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    •    Anembryonic pregnancy /blighted ovum – empty pregnancy
    •    Anencephaly – absent brain and cranial vault
    •    Ectopic gestation – outside the womb
    •    Heterotopic type of pregnancy – rare condition with 2 simultaneous gestations, one inside and another outside the womb
    •    Multiple gestation with discordancy/ demise – discrepancy in sizes and weights or a dead twin
    •    Molar pregnancy – abnormal type of pregnancy scanned as grape-like structures
    •    Ovarian cysts or myomatas causing abdominal enlargement.

    The above conditions show us the reason why early scan should not be put off; moreover, an FTS gives the expectant parents the heads-up on the prognosis of the gestation.

    Extensive researches have proven that the earliest scan gives the most accurate age of gestation due to the lack of factors affecting fetal size in the first trimester, thus couples should keep in mind that due date based on the age of the baby is determined in the FTS.

    The “Rule of 5”as early sonologic predictors of a viable pregnancy

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    •    5 weeks delayed from the first day of the last menstrual period (among women with regular monthly cycle), the first structure to become visible in the womb is the house of the coming baby or the gestational sac(GS) and is seen as a ring like structure through ultrasound with regular and thick borders.

    •    5 millimeters (half a centimeter) is the cut-off size of the yolk sac (YS), which is the second structure next to appear in a healthy pregnancy at 5.5 - 6 weeks of gestation. Likened to an egg yolk, it provides nutrient to the embryo. It is important to note that if YS increases in size more than 6mm., it becomes a macro-yolk sac which signifies accumulation of nutrient not utilized by the developing baby. Without the yolk sac, there would be no live embryo.

    •    5 millimeters is the size of the embryo (E) or crown rump length where a heart flutter becomes perceptible.  Larger than this measurement with no cardiac activity is an ominous sign.

    •    5 millimeters is the least measurement to be considered as the difference if the Sonologist is to compare between the sizes of the house (GS) and the baby. To put it simply, the smaller the house, the lesser is the fluid around the baby and is therefore detrimental for growth.

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    Second Trimester Scan (STS) at 14 to 28 weeks 

    The primary reason to seek STS among couples at this time is gender determination. But wait, you should learn more about the baby than just his/her genitals!

    Fetal Biometry

    Biometry which originates from the Greek word ‘metron’ which means to measure, is essential in ultrasound for its ability to assess fetal growth by measurement of the following body parts:
    •    Biparietal diameter (BPD) – 2 sides of the head
    •    Head circumference – roundness of the head
    •    Abdominal circumference – waistline of the baby
    •    Femur length –the baby’s thigh bone

    Congenital Anomaly Scan (CAS) at 20 to 24 weeks

    At 5 months, some fetal malformations are detectable through ultrasound. There again comes the emphasis on the word ‘some,’ as not all anomalies are identified at any given stage of pregnancy.  Nevertheless, a CAS aims to prepare both the parents and the fetus to early intervention if the need arises.

    One would opine though that a parent can never be emotionally prepared for an aberrant pregnancy.  However, it is through a targeted fetal organ imaging that a clear road map is drawn for early counseling and appropriate timing of delivery.

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    In addition to fetal biometry, a more detailed scan is focused on:

    •    Cranium – normal egg shaped fetal head, the profile (forehead, nose, chin alignment), signs of asymmetry/enlargement due to fluid accumulation
    •    Face – most notable is the cleft lip while palate is not always readily seen, symmetry of the orbits, tongue, mouth, ears
    •    Spine – normal curvature and rail-road tract appearance with absent outward flaring or protuberant masses
    •    Neck – nuchal cord loops, presence of solid or cystic masses
    •    Thorax (Chest) – 2/3 of its area is occupied by the lungs, rib contour, space defects, intactness of the diaphragm which separates the heart from the abdomen are other structures to be noted
    •    Heart – like the stomach, is seen at the left side, rule of thumb of its normal size is that 3 hearts could fit into the chest, the ‘offset cross’ appearance depicts the 4 chambers of the fetal heart
    •    Abdomen–wall defects like bowel loops extruded through the cord insertion
    •    Kidneys – paired ovoid structures whose length in millimeters is roughly equivalent to fetal age in weeks
    •    Urinary bladder – dark circular thing in between the fetal thighs filled with urine
    •    Skeleton – symmetry of extremities, complete number of fingers and toes

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    Third Trimester Scan (TTS) 

    A prenatal check usually consists of measuring the mother’s fundic height (approximate womb’s size by the use of tape measure) and listening to the baby’s heart beat by the stethoscope or Doppler, but as further studies have proven, the heart beat is last to disappear in the event that a baby loses water, stops breathing or is unable to move.  This is where the invaluable role of a Biophysical Score or Profile and a Nonstress Test comes in.

    3D/4D Scan at 26-32 weeks

    I can see my baby while urinating inside my womb through this new technology!

    •    Three dimension (3D) = Length + width + height (such as in 3D movies minus the special goggles)
    •    Four dimension (4D) = 3D + the actual time you are seeing the activities of your baby in the womb

    Image quality depends on a lot of factors namely:

    •    Maternal – such as the thickness or amount of fat in the mother’s abdominal wall
    •    Fetal – its position, the amount of fluid and space around the face and other body parts
    •    Machine – the latest models naturally give out the best resolution
    •    Scanner – the person’s expertise to perform and patience to wait for the baby to change its position into a more favorable one and the knowledge of operating the machine

    Having learned the most optimal time to undergo a scan, it is now time to have that first “peek“ through your womb and bond with your baby.

    Also by the author:
    “What you need to know about coiled umbilical cords”

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