I dont think there is an accurate way to distinguish various blood contents according to who secreted it.   The mother's hormones, cortisol, neurotransmitters go to the fetus,  and fetal hormones go into the maternal blood supply and it all gets mixed up, so  how can you determine  what came from whom?     The placenta is pretty much a passive transport medium, that does not interact much with either, and like the fetus, grows according to available nutrients, and does not grow when nutrients are lacking.     Does the fetus signal its needs to the mother?   Thats not what i was taught.  I was  taught, that the fetus is  an effective leach/parasite who takes whatever it needs from what is available.    If it could signal the  mother, I think the first thing the fetus would  say, is : Please Mom stop drinking cola, eating potato chips and  and smoking cigarettes.  I need more oxygen and less cortisol and stress.  Mom, dont drink so much alcohol,  and where women are short of protein intake, the fetus would say,  Mom, could you eat more protein, please?   

Did I misunderstand what you are asking?  I might be.

This question can't be answered in a few sentences, but there are a few articles about the maternal-placental-fetal interaction. Blood is not the only way to communicate, there exists also a communication in the amniotic fluid and chorion and amnion tissues.  I can recommand "Placental Stress Factors and Maternal-Fetal Adaptive Response" by Florio et al., PMID:12583606 or Petraglia et al. :Paracrine regulation of human placenta: control of hormonogenesis PMID:9786464.

If you are interested in the complete hormonal regulation for birth , you can find Sarah Buckleys book : "Hormonal Physiology of Childbearing:

Evidence and Implications for Women, Babies, and Maternity Care" for free here :

www.nationalpartnership.org/research.../hormonal-physiology-of-childbearing.pdf

Hope, that will help you !

The question asked what hormones are secreted by the fetus (the embryo does not secrete hormones ) but the citation Christoph Wohlmuth posted yesterday only mentions hormones secreted by the placenta. Kindly clarify.

Placenta. 2017 Jun;54:83-88.

Review: Fetal-maternal communication via extracellular vesicles - Implications for complications of pregnancies.

The human placenta is an organ that serves as the interface between the maternal and fetal circulation, thereby supplying the fetus with nutrients, blood and oxygen through the umbilical cord. During gestation, the placenta continuously releases several molecules into maternal circulation, including hormones, proteins, RNA and DNA. Interestingly, the presence of extracellular vesicles (EVs) of placental origin has been identified in maternal circulation across gestation.