Ultrasound dating of pregnancy

12-week scan

Due to the size of the developing structures and embryo, it is uncommon to perform an ultrasound before 5 weeks gestation 5 weeks after the start of your last menstrual period. Ultrasound is not consistently able to confirm viability and fetal heart activity before 6 weeks gestation, so unless there is an urgent need to have a scan earlier, most of these ultrasounds are performed after 6 weeks and ideally at 8 weeks for dating purposes. Urgent cases may still be performed earlier; please discuss this with your referring doctor. Your ultrasound may be performed transabdominally on the skin of the abdomen or transvaginally. Transvaginal ultrasound involves placing a thin transducer slightly thicker than a tampon into the vagina. The transvaginal ultrasound gives more detail to the examination as the ultrasound probe comes into closer proximity to the uterus womb. A transvaginal scan is optional for all patients, and it is your decision whether to proceed with that part of the examination. Ultrasound, both transabdominal and transvaginal, is considered to be safe during the first trimester of pregnancy. Your examination will be done by a sonographer who will introduce themselves and confirm your identity and the procedure you are having.

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The common first step will be a dating scan between weeks as we like to check your baby before 10 weeks. Before 7 weeks it may be too early to acquire this information. To obtain the best images possible, this scan is routinely performed internally and perfectly safe to perform during early pregnancy. At 7 weeks gestation a pregnancy sac should be seen within the uterus. Within this sac will be an embryo, heart motion and yolk sac should be visible. Approaching 8 weeks, early brain formation is identified with a black space in the head called the rhombencephalon.

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The results of ultrasound testing provide you and your health care provider with critical information about you and your baby. See below for descriptions of the information gathered from these two types of ultrasounds. Ultrasound uses high-frequency sound waves to create images of the inside of the body.

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Dating Scan Before 10 weeks

Calculate estimated due date EDD and gestational age based on : Conception date date of ovulation, egg retrieval, or insemination Date of 3-day embryo transfer Date of 5-day embryo blast transfer Due date by sonogram reverse due date calculator First day of last menstrual period month 1 January 2 February 3 March 4 April 5 May 6 June 7 July 8 August 9 September 10 October 11 November 12 December date 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 year Because the human egg is capable of fertilization for only 12 to 24 hours after ovulation the date of ovulation may be taken as being the date of conception. However, ultrasound determination of the date of ovulation has the same imprecision as does the ultrasound estimate of the gestational age and, therefore, a precise date of conception cannot usually be determined as with in vitro fertilization. In addition, although a woman is most likely to become pregnant if she has sex on the day of ovulation conception may also occur from live sperm still in her reproductive tract on the day of ovulation if she had sex for up to five days before ovulation [26,27].

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