Comparison Between the Conventional Malmström Extractor and a New Extractor with Silastic Cup

I wish to compliment Dr. Hammarstrdm and coworkers on their randomized comparative study of two vacuum-extractor models (Acta Obstet Gynecol Scand 1986;65:791). We gladly accept their main conclusion concerning the comparative maternal and perinatal safety of the two types of instrument investigated, but wish to make a comment as to their other findings. Dr. Hammarstrdm and his colleagues conclude that extraction is less time consuming when the Silastic cup is used. Although this conclusion can be accepted as correct because it is based on figures, it may nevertheless be misleading because in all probability the findings themselves were influenced by the investigators’ failure to standardize the two types of procedure. If, when they applied the Malmstrom cup, they had created negative pressure in a single step (and reached the same vacuum level) as they had done with the Silastic cup, the corresponding mean extraction times would probably have been comparable. Malmstrom ( I ) initially considered it obligatory to create the vacuum stepwise. Later, however, this rule was gradually discarded, even by Malrnstrom himself. We fully agree with Nyirjesi (2) and Bird (3) that slow stepwise induction of the vacuum is not necessary and that pulling can be started immediately after the desired level has been obtained, without any loss of effectiveness of the extraction and without enhancing the hazard to the fetus. As to the level of negative pressure, we follow Bird’s (3) advice and currently use the highest possible vacuum level when applying metal cups. The conclusion that the Silastic cup had a higher failure rate than the Malmstrom instrument is a truism which could have been anticipated on historical grounds alone. Indeed, Simpson’s Obstetric Air Tractor (4) never met the inventor’s expectations and the Silastic cup looks quite like a copy of Simpson’s