Dear Ann, As you know we have an Definition with the name of "Homeorhesis"  which there are some variation during pregnancy such as modification in tissues,

with a little search you can find some litterateurs in this area, sch as:

1:

Structure and function of mammalian tendon

DH Elliott - Biological Reviews, 1965 - Wiley Online Library

... For instance, towards the end of pregnancy there is a fall in the tensile strength of the foetal

2: in rabbit:

Reflex response of the rabbit hind‐limb muscle vascular bed to baroreceptor stimulation and its modification by pregnancy.

PW Humphreys, N Joels - The Journal of physiology, 1982 - Wiley Online Library

you can find some of the easily,

Best wishes,

Mehdi