first trimester scans

First Trimester

Ultrasound Sonogram

Baby developing inside you
over the weeks and months
early pregnancy ultrasound sonogram





  

First Trimester Scans

  
The first trimester is months one, two, and three of your pregnancy.
Below are scan pictures taken during the early weeks of pregnancy. Measurements taken at these early scans will help to; confirm a pregnancy, date the pregnancy and to see any problems that may occur in the pregnancy ( low lying placenta, twins etc.).


Scans for week:
 |  4  |  5  |  6  |  7  |  8  |  9  |  10  |  11  |  12  |  13  | 



early pregnancy sonogram scans
Scans in early pregnancy are usually performed in the first trimester around 12 weeks. You may have a earlier scan, if you are experiencing pain or bleeding for example or unsure of LMP dates.

Transabdominal ultrasound (TAU) and also the transvaginal ultrasound (TVU) are valuable diagnostic tools in obstetrics and gynecology.

Transabdominal ultrasound will provide a panoramic view of the abdomen and pelvis and is noninvasive, whereas transvaginal ultrasound provides a more limited pelvic view and requires insertion of a probe into the vagina.

Transabdominal ultrasound cannot reliably diagnose pregnancies that are less than 6 weeks gestation. Transvaginal ultrasound, by contrast, can detect pregnancies earlier, at approximately 4 to 5 weeks gestation. Prompt diagnosis made possible by transvaginal ultrasound can, therefore, result in earlier treatment.

It is recommended that all pregnant women have a scan in the first trimester, to establish the date when the baby is due, check the number of babies also the position of the placenta.

First trimester ultrasonic scans may show 'soft' markers for chromosomal abnormalities, such as the absence of fetal nasal bone or an increased fetal nuchal translucency (back of the neck) to enable detection of Down syndrome fetuses.

While your sonographer takes measurments they will explain what you are looking at. It may not be easy for you to make out what you are seeing on the screen in the early scans. The images below will give you an idea of what can be seen and what they look for at each week; of the first trimester.


Scans for week:
 |  4  |  5  |  6  |  7  |  8  |  9  |  10  |  11  |  12  |  13  | 


  

Week 4 Scan

Gestational Sac size = 3 to 6mm
 
gestational sac
4week doppler


The gestational sac first appears at about 4 weeks gestational age, and grows at a rate of about 1 mm a day through the 9th week of pregnancy.

It initially appears as a round, anechoic structure. In experienced hands, it may be detected as early as 30 days gestation by TVU.

At 4 weeks and 3 days, a tiny gestational sac becomes visible within the decidua.

While a gestational sac is sometimes seen as early as during the 4th week of gestation, it may not be seen until the end of the 5th week, when the serum hCG levels have risen to 2500 - 3500 mIU/mL.

Gestational Sac week 4 ultrasound scan

At this early stage of pregnancy, the gestational sac already contains the yolk sac, embryonic disk, and amnion, but these structures are too small to be visualized by sonography.

week4_sac

In these early first trimester scans, when no structures are visible within the gestational sac, gestational age (GA) may be estimated from the sac diameter. A common method is to measure the mean sac diameter (MSD), add 30 to the sac size in millimeters, to give gestational age in days.

By the time the embryo becomes visible on ultrasound the sac diameter is no longer accurate in estimating gestational age. If cardiac activity can be detected but the embryo is not measurable, the GA is about 5.5 to 6.0 weeks.

Week 4 Fetal Development
 
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Week 5 Scans

 
week 5 scan

Gestational Sac
size = 6 to 12mm
 

The Embryo is too small to be seen early in week 5, it is smaller than a grain of rice.
5weeks yolk sac


Gestational sac (black area) is seen. The yolk sac (small white circle at upper left of sac) is a source of nutrients for fetus.
5weeks 4days fraternal twins

Twin pregnancy (fraternal twins) Ultrasound
Pregnancy resulted from implantation of 2 genetically different embryos.
Yolk sacs and fetal poles (the early fetus) are seen in 2 completely separate sacs
week5 day4 mono twins

One gestational sac seen with 2 yolk sacs visible inside it Identical (monozygotic) twins.
This results from an early embryo dividing into 2 genetically identical embryos.
Fetus = approximately 1.25 mm long

An experienced sonographer can detect a yolk sac with transvaginal ultrasound when the gestational sac has reached a mean diameter of 8 mm to 10 mm. The presence of a yolk sac confirms the diagnosis of an intrauterine pregnancy and excludes ectopic pregnancy, except in rare cases of simultaneous intrauterine and extrauterine gestations.

The yolk sac is first visible at 5 weeks and it is always present by 5 weeks and 4 days. There are lacunary structures [cavities or spaces] at the site of implantation. The embryonic pole appears adjacent to the yolk sac, soon showing cardiac activity. Since the connecting stalk is short, the embryonic pole is found near the wall.

With transvaginal ultrasonography, cardiac motion can sometimes be seen in a 2-mm to 3-mm embryo, and is invariably detected in normal pregnancy when the length of the embryo reaches 5 mm. At the end of week 5, the heart rate is about 60 – 90 bpm.
In early pregnancies, the actual cardiac rate is less important than its presence or absence.

Week 5 Fetal Development
 
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Week 6 Scan

 
week6 ultrasound

Sac size = 14 to 25mm
CRL (crown to rump length)
= 4 to 7mm
Length = 0.2 to 0.3 inch
6 week

Close up week 6 — 3D scan
3D with arrows pointing to the embryo (CRL) The yolk sac lies adjacent to the embryo

6 weeks 4 days

Embryo cardiac ativity was seen with a heart rate of 126 bpm.

6w4d fetalpole

Fetus is between white cursors
A fetal heartbeat was seen during this scan

The fetal pole grows at a rate of about 1 mm a day, starting at the 6th week of gestational age. Thus, a simple and accurate way to "date the fetus" in an early pregnancy is to add the length of the fetal pole (in mm) to 6 weeks. Using this method, a fetal pole measuring 5 mm would have a gestational age of 6 weeks and 5 days.

Week 6 Fetal Development
 




More Ultrasound Scan Information:

Fetal growth percentile charts  |  Fetal Growth Percentile Calculator

Charts and tables for: - CRL - BPD - OFD - HC - HL - FL scan measurements.

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