Validation of Ultrasound Dating Protocols Using Data From Twins Conceived Through In Vitro Fertilization in Nova Scotia: A Retrospective Cohort Study

OBJECTIVES

Clinical practice guidelines recommend determining gestational age (GA) for twin pregnancies using the fetal crown rump length (CRL) of the larger fetus. This study investigated whether the CRL of the larger or smaller fetus at 11-14 weeks best predicted in vitro fertilization (IVF) assigned GA.

METHODS

A retrospective cohort study of twin pregnancies conceived by IVF ± intracytoplasmic sperm injection, 2004-2022, generated GA estimations for each co-twin CRL at the 11-14 week ultrasound, to determine which fetus (smaller or larger) more consistently predicted IVF-assigned GA. Monoamniotic twins and twins with known structural or vascular abnormalities were excluded. Paired t tests evaluated the ability of CRL to predict GA, and logistic regression evaluated the predictive ability of each of the co-twin groups with increasing size differences. Statistical significance was set at P < 0.05.

RESULTS

Viewpoint 6 identified 359 eligible twin pairs. CRL was closest with the smaller fetus (0.38 days); CRL for both the smaller (95% CI 0.16-0.61) and the larger (2.25 days, 95% CI 2.04-2.46) fetus showed deviation from IVF-assigned GA. As the absolute difference between the small and large fetus increased, the ultrasound-estimated GA of the smaller fetus was still consistently closer to IVF-assigned GA.

CONCLUSIONS

In this selected population of twins with known GA, the CRL of the smaller fetus more accurately predicted IVF-assigned GA even with increasing differences in fetal size. These findings provide important information for appropriately dating pregnancies to facilitate adherence to national guidelines to monitor for pregnancy complications, and plan frequency and type of fetal surveillance, as well as timing of delivery.

No. 375-Clinical Practice Guideline on the Use of First Trimester Ultrasound

OBJECTIVE

This guideline reviews the clinical indications for first trimester ultrasound.

OUTCOME

Proven clinical benefit has been reported from first trimester ultrasound.

EVIDENCE

A Medline search and bibliography reviews in relevant literature provided the evidence.

VALUES

Content and recommendations were reviewed by the principal authors and the Diagnostic Imaging Committee of the Society of Obstetricians and Gynaecologists of Canada. Levels of evidence were judged as outlined by the Canadian Task Force on Preventive Health Care.

RECOMMENDATIONS

No. 359-Obstetric Ultrasound Biological Effects and Safety

OBJECTIVE

To review the biological effects and safety of obstetric ultrasound.

OUTCOME

Outline the circumstances in which safety may be a concern with obstetric ultrasound.

EVIDENCE

The 2005 version of this guideline was used as a basis and updated following a Medline search and review of relevant publications. Sources included guidelines and reports by Health Canada and the American Institute of Ultrasound in Medicine.

VALUES

Review by principal author and the Diagnostic Imaging Committee of the SOGC. The quality of evidence and classification of recommendations have been adapted from the Report of the Canadian Task Force on the Periodic Health Examination.

BENEFITS, HARMS, AND COSTS

Obstetric ultrasound should only be done for medical reasons, and exposure should be kept as low as reasonably achievable because of the potential for tissue heating. Higher energy is of particular concern in the following scenarios: Doppler studies (pulsed, colour, and power), first trimester ultrasound with a long trans-vesical path (>5 cm), second or third trimester exams when bone is in the focal zone, when scanning tissue with minimal perfusion (embryonic), or in patients who are febrile. Operators can minimize risk by limiting dwell time and exposure to critical structures. It is also important to be aware of equipment-generated exposure information.

RECOMMENDATIONS

Reduction in neural-tube defects after folic acid fortification in Canada

BACKGROUND

In 1998, folic acid fortification of a large variety of cereal products became mandatory in Canada, a country where the prevalence of neural-tube defects was historically higher in the eastern provinces than in the western provinces. We assessed changes in the prevalence of neural-tube defects in Canada before and after food fortification with folic acid was implemented.

METHODS

The study population included live births, stillbirths, and terminations of pregnancies because of fetal anomalies among women residing in seven Canadian provinces from 1993 to 2002. On the basis of published results of testing of red-cell folate levels, the study period was divided into prefortification, partial-fortification, and full-fortification periods. We evaluated the relationship between baseline rates of neural-tube defects in each province and the magnitude of the decrease after fortification was implemented.

RESULTS

A total of 2446 subjects with neural-tube defects were recorded among 1.9 million births. The prevalence of neural-tube defects decreased from 1.58 per 1000 births before fortification to 0.86 per 1000 births during the full-fortification period, a 46% reduction (95% confidence interval, 40 to 51). The magnitude of the decrease was proportional to the prefortification baseline rate in each province, and geographical differences almost disappeared after fortification began. The observed reduction in rate was greater for spina bifida (a decrease of 53%) than for anencephaly and encephalocele (decreases of 38% and 31%, respectively).

CONCLUSIONS

Food fortification with folic acid was associated with a significant reduction in the rate of neural-tube defects in Canada. The decrease was greatest in areas in which the baseline rate was high.

Ultrasound evaluation of first trimester pregnancy complications

OBJECTIVES

First, to review normal embryonic development and the sonographic evidence of early pregnancy failure; second, to review sonographic evidence of ectopic pregnancy.

OUTCOMES

First, prediction of pregnancy failure, second, sonographic identification of ectopic pregnancy.

EVIDENCE

A MEDLINE search and review of bibliographies in identified articles was conducted.

VALUES

The evidence was reviewed by the Diagnostic Imaging Committee along with the principal authors. A quality of evidence assessment was undertaken as outlined in the report of the Canadian Task Force on the Periodic Health Examination (Table 1).

BENEFITS, HARMS, AND COSTS

Women presenting with first trimester bleeding may be incorrectly diagnosed with a missed abortion and (or) may be inappropriately reassured about viability. Transvaginal ultrasound provides improved resolution allowing description of early embryonic development characteristics. Improvement in the identification of the sonographic landmark of normal embryonic development and awareness of the sonographic risk factors of pregnancy failure may lead to more successful management strategies. Diagnosis of suspected ectopic pregnancy often involves an assessment of both hormonal markers and sonographic features. Maternal morbidity and mortality can be reduced with an early diagnosis of ectopic pregnancy.

RECOMMENDATIONS

There is good (class A) evidence that current ultrasound technology can distinguish between normal and abnormal pregnancies in the first trimester. There is good (class A) evidence that transvaginal ultrasound in conjunction with quantitative-HCG can diagnose ectopic pregnancy.

Prenatal infantile cortical hyperostosis (Caffey's disease): a 'hepatic myeloid hyperplasia-pulmonary hypoplasia sequence' can explain the lethality of early onset cases

BACKGROUND

Infantile cortical hyperostosis (ICH) is benign and self-limiting when it presents near or after birth but is usually lethal when it presents earlier.

METHODS

We present the clinical, ultrasonic, radiographic and pathologic findings in an instructive case of early onset prenatal ICH.

RESULTS

A 40-year-old G2P1 woman delivered spontaneously at 22 weeks' gestation. Prenatal ultrasounds showed rib and mandibular abnormalities as well as short humeri. Post-mortem radiographs showed asymmetric hyperostosis in long bones, mandible, scapulae and pelvis with sparing of spine, hands, feet and skull. The affected skeleton showed marked bony sclerosis and ballooning of the diaphyses of the long bones with periosteal sclerosis. A complete autopsy showed characteristic histologic findings in affected bones. Previous reports at 20+ weeks have described anasarca, fetal hydrops, hepatomegaly, and pulmonary hypoplasia. In our case, there was no hydrops/anasarca; hepatomegaly, due to massive extramedullary hematopoiesis with marked myeloid hyperplasia, combined with ribcage abnormalities, caused mild pulmonary hypoplasia.

CONCLUSION

We hypothesize that early onset fetal ICH is usually lethal because massive hepatic myeloid hyperplasia sequentially causes: (1) hepatomegaly and, in conjunction with rib abnormalities, mild pulmonary hypoplasia, (2) sinusoidal and pre-sinusoidal portal hypertension followed by ascites/hydrops, and (3) ascites/hydrops-induced severe pulmonary hypoplasia.

Ultrasound evaluation of first trimester pregnancy complications

OBJECTIVE

To review the biological effects and safety of obstetric ultrasound.

OUTCOME

Outline the circumstances in which safety may be a concern with obstetric ultrasound.

EVIDENCE

Medline was searched, and a review of a document on this subject published by Health Canada and of bibliographies from identified articles was conducted.

VALUES

Review by principal authors and the Diagnostic Imaging Committee of the SOGC. The level of evidence was judged as outlined by the Canadian Task Force on the Periodic Health Examination.

BENEFITS, HARMS AND COSTS

Obstetric ultrasound should only be done for medical reasons, and exposure should be kept as low as reasonably achievable (ALARA) because of the potential for tissue heating. Higher energy is of particular concern for pulsed Doppler, colour flow, first trimester ultrasound with a long transvesical path (> 5 cm), second or third trimester exams when bone is in the focal zone, as well as when scanning tissue with minimal perfusion (embryonic) or in patients who are febrile. Operators can minimize risk by limiting dwell time, limiting exposure to critical structures, and following equipment generated exposure information. Recommendations 1. Obstetric ultrasound should only be used when the potential medical benefit outweighs any theoretical or potential risk (II-2A). 2. Obstetric ultrasound should not be used for nonmedical reasons, such as sex determination, producing nonmedical photos or videos, or for commercial purposes ( III-B). 3. Ultrasound exposure should be as low as reasonably achievable (ALARA) because of the potential for tissue heating when the thermal index exceeds 1. Exposure can be reduced through the use of output control and (or) by reducing the amount of time the beam is focused on one place (dwell time) (II-1A). 4. All diagnostic ultrasound devices should comply with the output display standards (MI and TI) (III-B). 5. When ultrasound is done for research or teaching purposes, exposed individuals should be informed if either the MI or TI are greater than 1 and how this exposure compares to that found in normal diagnostic practice (III-B). 6. While imaging the fetus in the first trimester, Doppler and colour Doppler should be avoided (III-B).

Obstetric Ultrasound Biological Effects and Safety

This document has been archived because it contains outdated information. It should not be consulted for clinical use, but for historical research only. Please visit the journal website for the most recent guidelines.

Fetal Soft Markers in Obstetric Ultrasound

This document has been archived because it contains outdated information. It should not be consulted for clinical use, but for historical research only. Please visit the journal website for the most recent guidelines.

Incidence of open neural tube defects in Nova Scotia after folic acid fortification

BACKGROUND

With the goal of preventing open neural tube defects (NTDs), recommendations for folic acid supplementation before conception were introduced in Canada in 1994, and by November 1998 Canadian grain products were being fortified with folic acid. We wished to determine whether the annual incidence of open NTDs in Nova Scotia, including those in stillbirths and terminated pregnancies, changed after the introduction of either folic acid supplementation or fortification.

METHODS

For the 10-year period from Jan. 1, 1991, to Dec. 31, 2000, we retrospectively extracted the total number of births in Nova Scotia and the number of live births and stillbirths with open NTDs from the Nova Scotia Atlee Perinatal Database as well as the number of terminated pregnancies affected by NTDs from the Fetal Anomaly Database. We determined the total annual incidence of all open NTDs, and of the subgroups spina bifida and anencephaly, per 1000 births in the province during the periods before (1991-1994) and after (1995-1998) folic acid supplementation initiatives were begun but before folic acid fortification of grain products was implemented, and during the periods before (1991-1997) and after (1998-2000) fortification.

RESULTS

In the period after supplementation initiatives were begun but before fortification was implemented, the incidence of open NTDs did not change significantly: the mean annual rate was 2.55 per 1000 births during 1991-1994 and 2.61 per 1000 births during 1995-1997 (relative risk [RR] 1.02, 95% confidence interval [CI] 0.77-1.35). After the fortification was implemented the incidence of open NTDs decreased by more than 50%: the mean annual rate was 2.58 per 1000 births during 1991-1997 and 1.17 per 1000 births during 1998-2000 (relative risk 0.46, 95% CI 0.32-0.66).

INTERPRETATION

The recommendations for folic acid supplementation alone did not appear to succeed in reducing the incidence of open NTDs in Nova Scotia, whereas the fortification of grain products with folic acid did result in a significant reduction in the incidence.