Good news for pregnant women: You may suffer constant bouts of sickness, cravings, sore breasts and aching knees but your memory is probably improving.
Scientists have shown that female rats that have given birth do significantly better in memory tests than other female rats.
The researchers from the University of Richmond, Virginia, US, led by Dr Craig Kinsley, conducted two tests of learning and memory in which the animals were required to find their way through different mazes.
Those rats which had given birth took much less time to find their way through the mazes and locate the food rewards on offer. Even foster-mother rats which had been given the young of others to look after performed better than the rodents that had not mated or had any contact with offspring.
The team believe that the hormones produced during pregnancy, or the experience of giving birth and suckling pups, may cause physical changes in the brain that make it easier for the female rat to remember where things are.
"Neural activity brought about by pregnancy and the presence of pups may literally reshape the brain, fashioning a more complex organ that can accommodate an increasingly demanding environment," the team write in the science journal Nature.
The suggestion is that the mental stimulation of caring for newly-born offspring effectively re-wires nerve cells and boosts brain power. As a result, the mother rat is better able to cope with the demands of rearing her young such as remembering nest sites and food and water stores.
Rats are different to humans, of course, but as mammals we quite clearly share many brain functions. Previous research has already shown that raised hormone levels in female rats preparing to mate increase the concentration of neural connections in the hippocampus, a primitive part of the brain thought to be linked to memory.
Pregnancy raises levels of the hormones, oestradiol and progesterone, for an even longer period.
The researchers believe "rich sensory events" generated by caring for young are likely to affect brain structure as well as hormones. The stimulation that comes from suckling in particular probably reorganises connections in a part of the brain called the hypothalamus.