Description of fetal heart rate patterns at 20 to 24 weeks gestation

Hofmeyr, Franelise (2012-12)

Thesis (MMed)--Stellenbosch University, 2012.

Thesis

ENGLISH ABSTRACT: Introduction - Accurate computerized analysis of the fetal heart rate (FHR) pattern has become more feasible and clinically relevant in recent years. Taking into account advances in neonatal care resulting in a declining lower limit for fetal viability as well as research into fetal effects of maternal high risk behaviour and escalating intra-uterine exposure to harmful toxins and drugs, fetal heart rate patterns need to be more accurately described in earlier gestations than what is currently available in literature. With advancing technology it is becoming possible to accurately record and interpret the FHR patterns from gestations as early as 20 weeks' gestation. By using the Monica AN24 transabdominal electrocardiographic fetal monitor and product specific software, we analysed early FHR patterns according to the Dawes-Redman criteria, as used in later gestations. Methods - The aim of our study was to describe patterns of FHR (short-term variability, basal heart rate, accelerations and decelerations) at 20-24 weeks' gestation. Physiological data were obtained from the routine second trimester fetal assessment by the Monica AN24 monitor as used in the Safe Passage Study. As of December 31, 2009, 411 participants completed their first fetal assessment and met our inclusion criteria. Because our aim was the description of patterns in pregnancies with a normal outcome, we excluded all adverse neonatal outcomes, preterm deliveries, babies with low birth weights as well as cases where delivery data were lost. After recordings of poor technical quality were also removed from our data pool, 281 recordings remained for analysis. Results - Distinct FHR patterns and quantifiable parameters of heart rate variability were consistently observed. In contrast to what has previously been published, accelerations of the FHR and reassuring baseline variation are present from as early as 20 weeks. Conclusion - Information from this study provides an important foundation for further studies of early FHR patterns and it will help us better assess the fetus at a crucial age for indicators of good outcome at early delivery.

AFRIKAANSE OPSOMMING: Inleiding - Akkurate gerekenariseerde ontleding van die fetale hartpatroon het in die afgelope paar jaar meer tegnologies haalbaar met toenemende kliniese toepassing geword. Tans ervaar ons besondere vooruitgang in neonatale sorg en dus dalende grense vir vroeë lewensvatbaarheid in kliniese praktyk. Daar is ook 'n toename in navorsing oor moederlike hoë risiko gedrag tydens swangerskap en die effek hiervan op die ontwikkeling die fetus asook die neonatale uitkomste. Akkurater beskrywing van fetale hartpatrone in vroeëre gestasies as wat huidiglik in die literatuur beskikbaar is, is dus genoodsaak om die effekte van blootstelling op die fetus waar te neem. Met vooruitgang in tegnologie is dit nou moontlik om deur nie-indringende elektrokardiografie, fetale hartpatrone te registreer en te interpreteer van so vroeg as 'n swangerskapsdurte van 20 weke. Deur die gebruik van die Monica AN24 transabdominale monitor en produk-spesifieke programmatuur, kon ons vroeë fetale hartpatrone ontleed volgens die Dawes-Redman kriteria wat gewoonlik in later swangerskapsduurtes gebruik word. Metodes - Die doel van ons studie was die beskrywing van verskeie fetale hartpatrone (naamlik korttermyn variasie, basale hartspoed, versnellings asook vestadigings) rondom 20 – 24 weke swangerskapsduurte. Fisiologiese data is in die tweede trimester verkry deur die Monica AN24 monitor, soos gebruik word in die voortgaande Veilige Geboorte Studie by Tygerberg hospitaal. Tot en met 31 Desember 2009, het 411 deelnemers hulle eerste fetale evaluasie vir die Veilige Geboorte Studie gehad en ook voldoen aan die insluitingskriteria van hierdie projek. Aangesien ons fokus die beskrywing van hartpatrone in normale swangerskappe was, het ons alle nie-wenslike neonatale uitkomste, voortydse verlossings, babas met lae geboorte gewig asook gevalle waarvan die geboortedata nie beskikbaar was nie, uitgesluit. Alle opnames met sub-standaard tegniese kwaliteit is ook verwyder uit ons finale data vir ontleding, wat ons met 281 opnames gelaat het vir hierdie studie. Resultate - Duidelike fetale hartpatrone en meetbare afmetings is deurgangs opgemerk. In teenstryd met wat voorheen gedokumenteer is, is die teenwoordigheid van versnellings asook gerusstellende basislyn variasie meetbaar vanaf 20 weke gestasie. Samevatting - Informasie vanaf hierdie studie verskaf 'n belangrike grondslag vir verdere projekte in die ontleding van fetale hartpatrone met die fokus op ondersoek van vroeë voorspelling van goeie neonatale uitkomste.

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