Yolk sac fetal pole no heartbeat: Fetal Pole: Ultrasound, Anatomy & Function

In a previous blog we discussed the expected ultrasound findings in a normal intrauterine pregnancy. Variations from the expected pattern of development are worrisome or, if major, definitive for early pregnancy failure or miscarriage. These were discussed in a recent review article by Doubilet et al. (N Engl J Med 2013;369:1443-51). Here is a summary:

The criteria most often used to diagnose pregnancy failure are the absence of cardiac activity by the time the embryo has reached a certain length (crown–rump length), the absence of a visible embryo by the time the gestational sac has grown to a certain size (mean sac diameter), and the absence of a visible embryo by a certain point in time.

Crown-rump length (CRL)

A crown–rump length of 5 mm was widely recommended as a positivity criterion for diagnosing failed pregnancy when no cardiac activity is seen. Recent studies have shown that a 5-6 mm cutoff can result in a false positive diagnosis of pregnancy failure. It is now recommended that we use a 7 mm (rather than 5 mm) cut-off for diagnosing failed pregnancy. Thus if the crown-rump length is 7 mm and there is no heart beat visible, it is suspicious for a failed pregnancy.

Gestational sac diameter

It is prudent to use a cutoff of 25 mm (rather than 16 mm) for the mean sac diameter with no visible embryo in diagnosing failed pregnancy (see figure above). This would yield a specificity and positive predictive value of 100% (or as close to 100% as can be determined). When the mean sac diameter is 16 to 24 mm, the lack of an embryo is suspicious for, though not diagnostic of, failed pregnancy

Time based criteria for failed pregnancy

Not all failed pregnancies ever develop a 7-mm embryo or a 25-mm gestational sac, so it is important to have other criteria for diagnosing pregnancy failure. The most useful of such criteria involve non visualization of an embryo by a certain point in time. An alternative approach to predicting pregnancy failure, based on subnormal growth of the gestational sac and embryo, has been shown to be unreliable. Non visualization of an embryo with a heart- beat by 6 weeks after the last menstrual period is suspicious for failed pregnancy, but dating of the last menstrual period (in a pregnancy conceived without medical assistance) is too unreliable for definitive diagnosis of pregnancy failure.

The timing of events in early pregnancy — gestational sac at 5 weeks, yolk sac at 5 ½ weeks, and embryo with heartbeat at 6 weeks — is accurate and reproducible, with a variation of about ± ½ week; this consistency explains the time-related criteria for pregnancy failure. For example, if the initial ultrasonogram shows a gestational sac with a yolk sac and a follow-up scan obtained at least 11 days later does not show an embryo with cardiac activity, the diagnosis of failed pregnancy is established.

According to the Society of Radiologists in Ultrasound Multispecialty Consensus Conference on Early First Trimester Diagnosis of Miscarriage and Exclusion of a Viable Intrauterine Pregnancy, October 2012; the following are guidelines for Transvaginal Ultrasonographic diagnosis of Pregnancy Failure in a Woman with an Intrauterine Pregnancy of Uncertain Viability.

Findings Diagnostic of Pregnancy Failure

• Crown–rump length of ≥7 mm and no heartbeat
• Mean sac diameter of ≥25 mm and no embryo
• Absence of embryo with heartbeat ≥2 wk after a scan that showed a gestational sac without a yolk sac
• Absence of embryo with heartbeat ≥11 days after a scan that showed a gestational sac with a yolk sac

Findings Suspicious for, but Not Diagnostic of, Pregnancy Failure

• Crown–rump length of <7 mm and no heartbeat
• Mean sac diameter of 16–24 mm and no embryo
• Absence of embryo with heartbeat 7–13 days after a scan that showed a gestational sac without a yolk sac
• Absence of embryo with heartbeat 7–10 days after a scan that showed a gestational sac with a yolk sac
• Absence of embryo ≥6 wk after last menstrual period
• Empty amnion (amnion seen adjacent to yolk sac, with no visible embryo)
• Enlarged yolk sac (>7 mm)
• Small gestational sac in relation to the size of the embryo (<5 mm difference between mean sac diameter and crown–rump length)

When there are findings suspicious for pregnancy failure, follow-up ultrasonography at 7 to 10 days to assess the pregnancy for viability is generally appropriate. Treatments for early miscarriage are discussed here.

To see a fertility specialist who is a board-certified physician with high success rates, make an appointment at one of InVia’s four Chicago area fertility clinics.

Is no fetal heartbeat at 6 weeks of pregnancy a sign of miscarriage? –

Is no fetal heartbeat at 6 weeks of pregnancy a sign of miscarriage?

Miscarriage is one of the most stressful situations for a couple who are trying hard for conceiving. Such couples if achieve pregnancy but no fetal heartbeat is visible, can assume the condition as a miscarriage. Is it really so? In this blog, Dr. Nishant Dixit, a highly experienced Reproductive Medicine Specialist will explain how and at what time embryos grow in the uterus and what is delayed conception? Moreover, causes of no heartbeat at 6-week conception are also discussed, and how the couple should proceed in such a situation?

In 15–20% cases out of 100 pregnancies, the fetal heartbeat is not detected within 6 weeks of internal sonography. The situation can be very depressing because couples who have conceived but there’s no fetal heartbeat, such couples begin to panic as they generally interpret it as a pregnancy loss. Such couples always think about what can be done to bring the heartbeat of the baby. To understand the process of fetal heartbeat detection, it is important to know the timeline of naturally conceived pregnancy and how different milestones are achieved in the process.

Heartbeat detection in natural pregnancy

For example, if ovulation in women occurs on the fourteenth day, then after 5-7 days, the embryo begins to develop in the fallopian tube and thereafter it rolls down to the uterus and is implanted in the uterus wall. As soon as the embryo is implanted, the embryo’s cells begin to divide and secrete a hormone called beta-hCG. Due to the effect of this hormone, the woman stops menstruating.

At this time, four weeks of pregnancy are completed and if internal sonography is done at this time, then the membrane of the Gestational Sac should be visible in it. After 1 week, the Yolk Sac should also be visible inside the Gestational Sac. At 6 weeks the fetal heartbeat should be visible along with the yolk sac inside that g sac. This is a normal timeline for a naturally conceived pregnancy but sometimes in the case of late pregnancy, this timeline can change. For example, if ovulation occurs on the 18th or 20th day in a woman, then this timeline shifts 1 week further. The gestational sac is visible within 5 or 6 weeks instead of 4 weeks and the yolk sac appears in 6 or 7 weeks. The fetal heartbeat occurs at 7 or 8 weeks.

Heartbeat detection in IVF pregnancy

In some pregnancies, the exact time of implantation can be identified. For instance, pregnancy is achieved through Assisted Reproductive Techniques like In Vitro Fertilization (IVF). In the case of IVF pregnancy, the right time of implantation can be found out and at 6 weeks, fetal heartbeat can be detected. But if no heartbeat is seen, couples should wait for one week for the heartbeat to appear. This happens in 10-15% of cases. But if after one week also no heartbeat is visible, then there are no chances of fetal heartbeat and it can be a pregnancy loss. Such kinds of pregnancies are known as Blighted Ovum and no supportive treatment or medication is provided as there is a low possibility of a healthy pregnancy.

Why there is no heartbeat in a baby within 6 weeks of pregnancy?

This is one of the most common questions asked by couples. In 90% of cases, the genetic abnormality is one major reason. Thus, couples are advised to undergo genetic investigation, uterus examination, and blood tests along with some hormonal tests to find the accurate reason for the delayed heartbeat in the fetus.

In Brief

The couple should not worry in case the fetal heartbeat is not visible at 6 weeks in the internal sonography. This can be due to the late conception of pregnancy. It is suggested to wait for 1-2 weeks as there are good chances for detection of fetal heartbeat in case of delayed conception.

• Dr. Nishant Dixit
• DNB (OBGY), MNAMS
• Fellowship in Reproductive Medicine
• Director, Nishant Fertility Centre
• Reproductive Medicine Specialist

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Ultrasound indicators in early pregnancy

Ultrasound examination has become an integral part of obstetrics and it is difficult to imagine the management of pregnancy without this important method of examination. But with the growing popularity of ultrasound, problems arose: they began to be abused, and the more and more often ultrasound is performed, the more the practical value of this examination method is lost. Until now, the quality training of ultrasound technologists and ultrasound doctors with a specialization in obstetrics, that is, diseases and abnormalities in the development of the fetus (ultrasound perinatologists), has suffered. Such specialists are not enough all over the world. Interpretation of survey results is often difficult due to differences in reference values ​​in different hospitals, as well as in different countries. nine0003

Not so long ago, a study was conducted in Canada to evaluate the accuracy of measuring the thickness of the placenta, and it turned out that the measurement error by different doctors in the same medical institution was 1-3 cm, and among European doctors these discrepancies were even greater. The human factor plays an extremely important role in the conduct of the survey, but so far, the development of the medical staff has been slow and inefficient.

Although most pregnant women trust their doctors, more and more often they have to double-check the results of the examination and the rationality of the prescribed treatment. In the post-Soviet countries, many ultrasound specialists intervene in the process of pregnancy management, giving recommendations and even prescribing treatment, which is not practiced in most countries of the world. The worst option is when the conclusion completely contradicts the measurements of the size of the fetus and other pregnancy parameters. Many ultrasound doctors practice creating a diagnosis “out of nothing”: against the background of normal indicators, fictitious diagnoses of some violations are made in the conclusion. A number of diagnoses are generally not recognized in modern obstetrics, for example, “uterine hypertonicity.” Therefore, having received a “terrible conclusion” and a negative prognosis when refusing treatment (usually with many ineffective fuflomycin drugs), many pregnant women dive into the Web in search of ultrasound examination data in order to compare their results with the “Internet”. The most common question that sounds in such cases is: “How dangerous is this and will I be able to carry a pregnancy?” nine0003

The work of ultrasound specialists is now simplified by the fact that many indicators are compared with reference values ​​automatically – through programs embedded in ultrasound machines. The task of an ultrasound specialist is to correctly and accurately take measurements. Since the fetus is small, especially in early pregnancy, measuring different parts of the ovum and fetus can be difficult. A small error of just 1 mm can create a stressful situation when interpreting indicators and choosing pregnancy management tactics. Also, keep in mind that many of the reference values ​​were derived from small clinical trials several decades ago, in the early days of ultrasound in obstetrics. Therefore, now the indicators of norms and deviations are being revised, taking into account the physiological changes in the progressing pregnancy and the growing fetus, depending on the period. nine0003

However, many pregnant women need accurate information to help them evaluate their ultrasound results without the help of a doctor. Often women ask which type of ultrasound is better to perform: transvaginal (TV) with vaginal probe or transabdominal (TA) probe for abdomen ? There is no difference in choosing a sensor – it all depends on the skills of the doctor and his ability to take measurements correctly. With the progress of pregnancy, a combination of sensors is used if necessary.

Another error of doctors and pregnant women is constantly observed when calculating the gestational age. Remember: there is one type of gestational age – obstetric, and it is always expressed in weeks and days , not months. Sometimes, especially in the first weeks of pregnancy, it is called the menstrual period. Embryonic term does not exist! Ultrasound specialists are mistaken when they tell women that the period is determined by the size of the embryo, which means that it supposedly differs from the menstrual period (on the first day of the last menstruation with regular menstrual cycles of 26-30 days). Any ultrasound machine calculates the period adjusted for the duration of menstruation and the size of the fetal egg and embryo, and this is always an obstetric period. The date of the expected birth is also calculated according to the obstetric gestational age. nine0003

Ultrasound in the first trimester is performed to:

• confirm uterine pregnancy;
• confirmation of a live or missed pregnancy;
• confirmation or exclusion of ectopic pregnancy;
• determining the duration of pregnancy;
• as part of prenatal genetic screening.

There are three phases of pregnancy, which can and should be monitored by ultrasound picture of the stages of development of the fetal egg, embryo and fetus. nine0003

1. Conception or conception phase – first 3-5 weeks. It starts from the moment of conception – approximately 2 weeks after the first day of the last menstruation – and the appearance of the fetal egg, which is not always possible to detect using ultrasound during this period.
2. Embryonic phase – 6-10 weeks when the embryo can already be detected.
3. Fetal phase – from 10-12 weeks, when the embryo becomes a fetus and the process of laying and initial development of all organs and organ systems is completed. nine0028

Basic ultrasound parameters of normal pregnancy in the first trimester

Early pregnancy is confirmed by the presence of three important structural units:

• gestational sac;
• yolk sac;
• fetal (or embryonic) pole.

Additional signs of uterine pregnancy: detection of a double decidual sac and a symptom of a double bubble (ultrasound terms that may not be memorized by people without a medical education, but which are important to focus on when performing ultrasound in the early stages). nine0003

A gestational sac or gestational sac (GM)

The presence of a gestational sac is the first ultrasound sign of pregnancy. Up to 5 weeks of pregnancy (from the last day of menstruation), it is most often not possible to see the presence of an embryo in a fetal egg. By determining the size of the fetal sac, the gestational age can be set with an accuracy of 1 week (+/- 1 week). When an embryo is detected, the size of the ovum for determining the gestational age is of no practical importance. nine0003

In obstetrics two indicators are used to determine the duration of pregnancy by measuring the size of the ovum:

1) the diameter of the gestational sac – only one measurement is carried out;

2) the average diameter of the gestational sac – determine the internal diameter of the ovum in three dimensions and calculate the average.

The gestational sac can be seen in:

• 4 weeks and 3 days from the first day of the last menstrual period on TV ultrasound and is usually 2–3 mm in diameter; nine0028
• 5-6 weeks from the first day of the last menstrual period on TA ultrasound, and its diameter is about 5 mm.

Calculation of term by the size of the ovum:

Menstrual gestational age = Mean diameter of the fetal egg (mm) + 30 or 35 (if the diameter is less than 16 mm)

For example, the average diameter is 5 mm, gestational age = 5 + 30 = 35 days, or 5 weeks.

Normal growth rate

Fertilized egg grows by an average of 2 mm every 2 days from 4th to 9th-th week of pregnancy, but such indicators are usually not used to determine the progress of pregnancy, but are used only to confirm the diagnosis of its regression (fading).

What to look for

If no embryo can be detected with a gestational sac of 16–24 mm, suspect a miscarriage or an empty gestational sac and repeat the ultrasound in a week.

The size of the fetal egg is more than 25 mm and the absence of an embryo speaks in favor of a pathological pregnancy (frozen, empty fetal egg). nine0003

If the size of the ovum decreases in the presence of a live embryo after 9 weeks, oligohydramnios can be suspected, although amniotic fluid level is usually not performed until 18–20 weeks.

Yolk sac

Before the embryo is born, the yolk sac, an important structure of the fetal egg, can be seen by ultrasound. The yolk sac is a 100% confirmation of the presence of a uterine pregnancy. With an ectopic pregnancy in the uterine cavity, you can find a formation that is somewhat reminiscent of a fetal egg, which is a specific reaction of the endometrium to pregnancy. nine0003

The yolk sac is located between the amnion and the chorion (two formations of the fetal egg, from which the fetal membranes and the placenta are formed) – in the chorionic space.

Normally, with an average diameter of the ovum of 5 mm, the size of the yolk sac is up to 6 mm (on average, 3–5 mm). The maximum size of the yolk sac is observed at 10 weeks and is 5–6 mm. During the laying and development of the organs of the embryo, the yolk sac is partially used in the formation of the intestine.

Amnion

Amnion is a shell (membrane) inside the ovum that contains the fetus. You can consider the fetal membrane up to 12 weeks of pregnancy with a fetus size of 5–7 mm. The completion of the formation of shells occurs by 12–16 weeks.

Coccyx-parietal size (KTR, CRL)

The coccyx-parietal size is the greatest length of the embryo, but significant errors are possible in measuring the size of the embryo. In the short term, when the limbs are poorly visible, it is more difficult to see the coccyx. By measuring this size of the embryo, a more definite gestational age can be set – up to 4 days. nine0003

With ultrasound, an embryo measuring 1–2 mm can be seen with a gestational sac measuring 5–12 mm at 5–6 weeks of gestation. During the day, the size of the embryo increases by 1 mm. A difference of 5 mm between the size of the embryo and the fetal egg is considered the minimum norm for pregnancy.

Calculation of gestational age

• Menstrual period in weeks = CTE (cm) + 6 (if CTE is less than 1 cm)
• Menstrual period in weeks = CTE (cm) + 6.5 (when CTE is greater than 1 cm)
• Menstrual period in days = CTE (mm) + 42 (with CTE up to 84 mm)

Embryo heartbeat

Embryo/fetal heartbeat can be detected at 6 weeks of gestation with embryo sizes greater than 2 mm, which is a reliable sign of a live pregnancy. However, in embryos up to 5 mm (TV ultrasound) and 9 mm (TA ultrasound), the heartbeat may not be noticed, therefore, in such cases, it is advisable to repeat the ultrasound after 3-5 days.

Before 6 weeks of gestation, the fetal heart rate is 100-115 beats per minute. Within 6–9th weeks, the frequency increases and reaches a maximum at 8 weeks – 144-159 beats per minute. Starting from 9 weeks, the frequency slowly and slightly decreases.

Slow heart rate is called bradycardia . However, it can also be a sign of fading pregnancy.

Bradycardia is set if:

• heart rate is less than 80 beats per minute with CTE less than 5 mm;
• less than 100 beats per minute at CTE 5–9 mm;
• less than 110 beats per minute at CTE 10-15 mm. nine0028

Collar zone (collar space, OT, NT)

Collar zone is an accumulation of lymphatic fluid between the skin and soft tissues of the embryo behind the neck (in the collar region), the thickness of which is a prognostic indicator of chromosomal abnormalities of the fetus. It is measured at 11-14 weeks (up to 13 weeks 6 days) – this is part of the first trimester prenatal genetic screening, which also includes the determination of biochemical markers in the mother’s blood. nine0003

Since the size of the neck crease depends on the size of the embryo, it is very important to measure within the limits of the gestational age – then the measurements will be not only accurate, but also of practical importance. That is, they do it with a CTE of 45–84 mm (11–14 weeks). Such a strict framework for taking measurements is associated with the peculiarities of the anatomical changes in the developing embryo, especially the lymphatic system and the exchange of lymphatic fluid.

Normal dimensions of the VZ are up to 3 mm. Pathological are considered sizes of 5 mm or more at 16-18 weeks, 6 mm or more – at 19-24 weeks.

In contrast to the nuchal space, which is measured in the first trimester, the thickness of the neck roll is measured in the second trimester . The neck roll is the distance between the outer edge of the occipital bone and the skin of the fetal neck. In many cases of chromosomal anomalies, especially those accompanied by malformations of the cardiovascular system, there is a violation of lymph metabolism and it accumulates in the region of the neck roll. Measurements are taken at 16–20 weeks (usually as part of an anatomical ultrasound), and measurements greater than 6 mm are abnormal. nine0003

Nasal ossicle

The presence or absence of the nasal ossicle and its length are recognized as markers for trisomy 21 (Down syndrome). Length is measured at 11–14 weeks as part of prenatal genetic screening. The absence of a bone or its length less than 2.5 mm may be signs of Down syndrome.

There are other ultrasound signs that are used by specialists to clarify the normal development of pregnancy or abnormalities, including miscarriage, empty gestational sac and others. nine0003

Starting from the second trimester (after 14-16 weeks), all measurements of certain parts of the fetus, as well as various indices that are calculated based on these indicators, are plotted with initial percentile curves (95%, 50%, 5% ), which were obtained by statistical processing of data from numerous measurements of fetuses in the past to determine the normal growth and development of this fetus. Creating individual graphs of important ultrasound indicators allows you to see the development of the child in dynamics and evaluate it more correctly. nine0012