Ultrasound in first trimester of pregnancy-Importance,Use,Indications

  • May 3, 2021

Written by
Dr Himani Gupta
Consulting Gynecologist in Kharghar, Navi Mumbai


-At the outset let me tell you that diagnostic ultrasound has been deemed safe for human embryo 

-Route of ultrasound can be transabdominal or trans vaginal. 

-For trans-abdominal scan full bladder is a requirement. 

-Lady should have drunk lots of water before coming for ultrasound.

-In trans vaginal scan full bladder is not required. 

-In both cases pregnant women can have food before coming ,fasting is not required


-A gestation sac as the name suggests is a small sac like structure within endometrial cavity and is the first sonography evidence of pregnancy. 

-Visualisation of the yolk sac- a ring like structure alongside embryo confirms with certainty

intra-uterine location of pregnancy and rules out ectopic pregnancy.

-Generally, by fifth week of pregnancy you can see the sac.

-An embryo and yolk sac are identified by 6th week of pregnancy and in transvaginal scan you 

may detect fetal heartbeat too.


-It’s a medical fact that beginning of life that is fertilization- in common man language meeting of ova with sperm happens in fallopian tube. 

-Afterwards the embryo travels the length of the tube and comes and get implanted in the uterus where it will grow to be a baby. 

-If anywhere this process is hampered and embryo gets stuck and does not reach the uterine 

cavity but continues to grow, we get ectopic pregnancy.

-Most common site is fallopian tube.

-Now this is a potentially dangerous medical situation as the growing embryo will cause rupture

 of wall of fallopian tube and in turn will lead to life-threatening bleeding inside the abdomen.

-High clinical suspicion and timely ultrasound will diagnose this condition so that corrective 

surgery can be done to save woman’s life.


-Heart beats in an embryo can usually be heard once the embryo length has reached 5 mm. 

-If an embryo length is 7mm and we still can’t hear fetal heartbeat we can repeat an ultrasound in one week’s time

-Once 10 mm size of embryo is reached and we still can’t find heartbeat, it is declared missed 

abortion and termination of pregnancy is offer


-Dating of pregnancy meaning finding out by sonography the approximate due date, is done by measuring Crown rump length of foetus,that is commonly known as CRL.

-In this foetus is measured from top of head to the lowest point of its buttocks.

-In this measurement yolk sac and Limb buds are not measured.

-This is a very important step as it gives us dating of pregnancy with variance of only three to five days.


-Multifetal gestation is when the lady is pregnant with more than one foetuses.

-If it is two in number it is a twin pregnancy.

-Triplet means 3 and quadruplet means 4

-Such pregnancies demand more medical surveillance and specialised care of pregnant  mother as there are increased risk of preterm and underweight birth in these cases.

-Amnionicity means how many gestation sacs are there and chorionicity means how many     placentae are there.

-This information helps the Gynecologist in deciding management protocols

-When advanced fertility treatments are used, like medicines are given to the woman to make her ova grow or at the time of ovulation washed and prepared semen is put inside uterine cavity the process which is known as IUI- that is intrauterine insemination.

-Or couple opts for test tube baby or IVF conception- in all these situations chances of multifetal gestation is more.


-The woman may have achieved pregnancy normally or with medical assistance but foetus did 

not continue to grow.

-It may be that fetal heart activity never appeared.

-It may be that it came but then disappeared.

-These medical conditions are known as missed abortion, anembryonic pregnancy or early fetal demise.

-It is nature’s way to cause expulsion of dead products leading to vaginal bleeding and lower abdominal pain in a pregnant woman.

-At times it may happen that products are not completely expelled.

-To diagnose all these conditions ultrasound is the investigation of choice so that further treatment of DNC, check curettage or cleaning of uterus can be offered.


-If women previous has previously given birth to a baby with structural abnormalities and she is 

again, pregnant we can look for some major abnormalities in first trimester.

-An anomalous condition known as Anencephaly can be diagnosed.

-In this condition fetal skull bones are absent and fetal brain matter is exposed

-Many heart defects can also be picked up.

-If such life-threatening conditions of foetus are diagnosed early in pregnancy termination can be offered.

-At the same time, it should be understood that with current technology it is not realistic to expect that all major abnormalities detectable in second trimester anomaly scan will be visualised in first trimester.

-Doing anomaly scan between 18 to 20 weeks of pregnancy is very important.


-Nuchal translucency or popularly known as NT represents the maximum thickness of the subcutaneous translucent area between the spine and soft tissue overlying the fetal spine at the back of the neck.

-It is measured in sagittal plane between 11th and 14th week.

-Presence of nasal bone in the foetus is also assessed.

-When the NT is increased or nasal bone is absent, the risk for fetal aneuploidy- trisomy 21 or 

Down’s syndrome and various structural anomalies like fetal heart defects are increased.

-Afterwards double marker is done, and in maternal blood two hormones beta HCG and PAPP-A (Pregnancy Associated Plasma Protein A) are done for further evaluation.


-We have already seen importance of NT, NB scan that is nuchal translucency and nasal bones 

scan along with double marker.

-If these investigations report is abnormal and the want to know for sure about wellbeing of fetus, we need to do ultrasound guided Chorion Villus Sampling and send this material for chromosomal analysis.


-Gestational trophoblastic disease is an abnormal pregnancy in which placental component trophoblast grows abnormally and forms multiple cysts like structure in the uterus.

-Fetal components are either completely absent or present only partially.

-Pregnancy related hormone beta HCG gets secreted in very large quantities in this condition ,

giving rise to excessive pregnancy symptoms like vomiting.

-Woman can also have pain and bleeding.

-This condition is easily diagnosed by ultrasound and evacuation of uterus is done.


-At times it is seen that despite having copper-T or multiload device inside the uterus woman 

has still conceived.

-Removal of the device becomes mandatory and is greatly assisted by sonography.


-When the woman becomes pregnant it is also very important to know that the structure of uterus is normal.

-If woman has some congenital uterine abnormalities, she requires specialised treatment to help her continue with pregnancy.

-If there are fibroids in uterus then also extra care is required.

-Ovarian cyst and endometriotic chocolate cyst also make special cases in pregnancy.

-Ultrasound or sonography helps in diagnosing these conditions

-We discussed about how sonography or ultrasound helps the Gynecologist in diagnosing so many conditions and making appropriate plans for treatment.

Early diagnosis by help of Ultrasound /Sonography is the key.


3 comments on “Ultrasound in first trimester of pregnancy-Importance,Use,Indications

  1. Dr. Nisha Hariharan, Consultant Breast Oncosurgeon, Apollo. says:

    Such an interesting read!
    A complex topic explained in a very simple and lucid manner. It is bound to be useful for many young expectant mothers and doctors alike.
    Great post Dr. Himani Gupta!

  2. Dr. Nisha Hariharan, Consultant Breast Oncosurgeon, Apollo Hospital says:

    Brilliant article, Dr. Himani Gupta !
    A complex topic explained in a very clear and lucid manner. It is bound to be useful to many young expectant mothers and doctors alike. MyGynaecWorld truly bridges a gap we all face today, authentic information explained with clarity in a simple language. Look forward to your next one.

  3. Dr. Nisha Hariharan, Consultant, Breast Oncosurgeon, Apollo Hospital says:

    Brilliant article, Dr. Himani Gupta !
    A complex topic explained in a very clear and lucid manner. It is bound to be useful to many young expectant mothers and doctors alike. Mygynaecworld.com truly bridges a gap we all face today, authentic information explained with clarity in a simple language. Look forward to the next one.

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