Trisomies 18 and 13: trends in prevalence and prenatal diagnosis - population based study.

OBJECTIVE: The objective of this study was to determine trends in prenatal detection and current estimates of prevalence for trisomies 18 (T18) and 13 (T13) and their implications for screening policy. METHODS: We conducted a cohort study from a population-based regional anomaly register covering 995 003 births (1995-2009). RESULTS: There were 786 affected cases. Total prevalence of T18 increased from 3.95 in 1995-1999 to 6.94 per 10 000 births in 2005-2009 (annual trend χ(2) = 25.99, p < 0.001) and live birth prevalence, when adjusted for in utero attrition, increased from 1.47 to 2.30 per 10 000 births over the same time (annual trend χ(2) = 6.36, p = 0.01). For T18 and T13 combined, the proportion of cases diagnosed by prenatal karyotype or suspected by ultrasound increased from 85.1% (165/194) in 1995-1999 to 95.2% (299/314) in 2005-2009 (p < 0.001). In 2005-2009, 50.3% of prenatal cytogenetic diagnoses for T18 and 38.5% of T13 were made after the discovery of first trimester ultrasound anomalies, and the majority, 56.4% (185/328), of affected pregnancies were karyotyped or had ended before 18 weeks. CONCLUSION: T18 is increasing in prevalence because of maternal age and earlier surveillance. Prenatal diagnosis occurs mostly in the first trimester, without the intrinsic structures of a formal screening programme. These findings support the extension of first trimester combined screening to include T18 and T13.

Intrauterine growth retardation.

IUGR puts the fetus at risk of stillbirth, perinatal morbidity and neonatal handicap, yet most instances of IUGR are not recognized. Progress has been made in recent years to monitor the high-risk fetus with intensive biometric and biophysical tests and to determine the appropriate time for intervention. These methods of surveillance are ineffective and inappropriate for population screening, and the main problem remains how to identify the at-risk fetus. Improvement of current performance requires the establishment of appropriate standards by which intrauterine growth can be assessed, and their introduction as part of well-organized screening programmes. We describe a computerized method of predicting the optimal weight for each pregnancy, which is individually adjusted for non-pathological variables such as maternal height, booking weight, ethnic group and parity. The optimal birthweight determines the expected slope or velocity of fetal weight gain. This individualized prediction improves the distinction between constitutional and pathological smallness. Furthermore, preterm weights are measured against a fetal weight norm rather than a birthweight standard that is derived from non-physiological preterm deliveries. The customized growth chart allows screening for growth retardation by determining the growth velocity through serial measurement and plotting of fundal height, backed up as necessary by ultrasound estimation of fetal weight and referral for more intensive surveillance as indicated.

Artifacts in fetal pulse oximetry: nonarterial pulsatile signals.

OBJECTIVE: We wished to investigate the effect of caput succedaneum on pulse oximetry readings. STUDY DESIGN: Oxygen saturation was measured by reflection pulse oximetry on various sites of scalps of 18 healthy neonates. The pulse rate obtained from the oximeter was checked against the heart rate from the electrocardiogram to see whether they were in agreement and synchronized. RESULTS: Nonsynchronized saturation values had a much wider range (30 to 97 vs 70 to 98) and a significantly lower mean (70 vs 84) than did synchronized values. Synchronized readings were obtainable in all 18 subjects over the temporal region but in only 39% of cases over the occipital region. Fourteen neonates had caput succedaneum, and in nine (61%) of these synchronized readings were not possible. It was noted that falsely low saturation values can be derived from pulsating waveforms, which have a slower rate than the electrocardiogram rate. CONCLUSIONS: The observed low pulsation rate is either of venous origin or represents modulated transmission of arterial signal through an edematous or congested scalp. This artifact will result in nonarterial oxygen saturation readings, and its exclusion is of importance in the development of pulse oximetry for intrapartum monitoring of the fetus.

Artifacts in fetal pulse oximetry: incomplete sensor-to-skin contact.

OBJECTIVE: Our purpose was to investigate apposition of reflectance sensors as a possible source of artifact in fetal pulse oximetry. STUDY DESIGN: A laboratory model was created to examine the effect of varying the distance of a reflectance probe from a subject's finger. The setup used two wavelengths (660 and 940 nm) and pulsatile (AC) and nonpulsatile signals (DC). An investigator's finger was stabilized in a purposely built mold from where the distance between skin and sensors could be varied in 1 mm steps. RESULTS: The AC and DC components of the signal react differently to increasing the distance between sensor and skin. The overall effect is that the ratio [formula: see text] increases with skin to sensor distance, which results in falsely low readings of oxygen saturation. CONCLUSIONS: Poor sensor-to-skin contact in reflectance pulse oximetry may cause false readings despite the presence of good waveforms and hence go unrecognized. Probe and software design needs to be able to identify and exclude such artifact before this technique can become useful for intrapartum fetal monitoring.

Adaptation of pulse oximetry for fetal monitoring during labour.

Application of pulse oximetry to intrapartum monitoring was investigated in 105 women. No adequate reading could be obtained in 44 cases. Two major sources of artifact, related to probe apposition and signal processing, were identified and excluded. The average arterial oxygen saturation from the fetal scalp was 82% (SD 6%), which is higher than has been inferred from pO2 levels. Readings below 60% or the development of an unstable baseline suggest the presence of substantial hypoxia and acidosis.