started work on introduction and background

thesis/sections/background.tex

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+%! Author = alex
+%! Date = 3/7/25
+
+
+\section{Background}\label{sec:background}
+
+\subsection{Physiological Background}\label{subsec:physiological_background}
+\subsubsection{Menstrual Cycle}\label{subsec:menstrual_cycle}
+The menstrual cycle describes the physiological changes in the female body that prepare it for pregnancy.
+It is divided into two phases: the \textbf{follicular phase} and the \textbf{luteal phase}.
+\\
+During the follicular phase, the ovarian follicles mature, and the endometrium (the inner lining of the uterus) thickens
+in preparation for a potential implantation of a fertilized egg.
+Around day 14 of a typical cycle, ovulation occurs, marking the transition to the luteal phase.
+Ovulation refers to the rupture of the mature ovarian follicle and the release of an egg cell into the fallopian tube.
+Figure\ref{fig:background_basic_female_reproductive_system} illustrates the female reproductive system,
+including the ovaries and the fallopian tubes.
+\\
+\begin{figure}
+    \centering
+    \includegraphics[width=0.4\textwidth]{background_female_reproductive_organs}
+    \caption{The basic female reproductive system\cite{wikimedia_commons_basic_2019}.}
+    \label{fig:background_basic_female_reproductive_system}
+\end{figure}
+Ovulation is triggered by a surge in \textbf{luteinizing hormone (LH)}
+and \textbf{follicle-stimulating hormone (FSH)}, following a peak in estradiol levels.
+As ovulation occurs, estradiol levels drop, progesterone levels begin to rise and a slight increase in body temperature
+(typically around 0.5°C) can be observed.
+This marks the beginning of the luteal phase.
+\\
+During the luteal phase, the endometrium thickens further, creating an optimal environment for embryo implantation.
+LH and FSH levels decrease, while progesterone remains elevated to support endometrial maintenance.
+If fertilization does not occur, progesterone levels drop, leading to the shedding of the endometrial lining along
+with the unfertilized egg.
+This process, known as menstruation, marks the beginning of a new cycle.
+\\
+The menstrual cycle typically lasts around 28 days, with ovulation occurring near the midpoint.
+However, variations, particularly in the follicular phase length, are common and can be influenced by factors such as stress, diet, exercise and age\cite{silberstein_physiology_2000}.
+Figure~\ref{fig:background_menstrual_cycle_physiology} provides a detailed overview of the hormonal and physiological changes
+throughout the menstrual cycle.
+
+\begin{figure}
+    \centering
+    \includegraphics[width=0.7\textwidth]{background_menstrual_cycle_physiology}
+    \caption{Physiological changes during the menstrual cycle\cite{pedroso_menstrual_2022}.}
+    \label{fig:background_menstrual_cycle_physiology}
+\end{figure}
+
+\subsubsection{Fertility Prediction}\label{subsec:fertility_prediction}
+Throughout the menstrual cycle, the chance of fertilization varies significantly.
+An egg cell released from the ovary during ovulation, can be fertilized for up to 24 hours.
+However, since male sperm cells can survive up to 6 days inside the female reproductive tract,
+the fertile window is typically defined as the five days before ovulation until one day after ovulation\cite{dunson_day-specific_1999}.
+Research by \citeauthor{dunson_day-specific_1999} has shown that the highest chance of fertilization is around one day before ovulation,
+as illustrated in Figure~\ref{fig:background_pregnancy_chance}.
+
+\begin{figure}
+    \centering
+    \includegraphics[width=0.8\textwidth]{background_pregnancy_chance_over_time}
+    \caption{Chance of fertilization depending on the day of the menstrual cycle.
+    The highest chance is around one day before ovulation\cite{dunson_day-specific_1999}.}
+    \label{fig:background_pregnancy_chance}
+\end{figure}
+
+It is important to note that fertility prediction is inherently dependent on ovulation prediction.
+Since the probability of conception is tightly linked to ovulation timing, the accuracy of fertility prediction methods
+is constrained by the precision of ovulation detection.
+This relationship underscores the necessity of developing reliable ovulation prediction models,
+as even small inaccuracies can significantly impact fertility assessments.
+
+\subsubsection{Physiological Signs of Ovulation}\label{subsec:physiological_signs}
+Several physiological signs correlate with ovulation and can be used for prediction.
+As shown in Figure~\ref{fig:background_menstrual_cycle_physiology}, these include hormonal fluctuations (LH and FSH surges) and
+changes in body temperature.
+Additionally, variations in cervical mucus consistency, salivary ferning patterns,
+and electrical resistance of the skin and vaginal mucosa have been observed\cite{silberstein_physiology_2000}.
+
+Among these, ultrasonography provides the most accurate confirmation of ovulation by detecting follicular changes,
+but it is costly and requires specialized equipment.
+Hormone measurements in urine and blood are widely used and available in at-home test kits,
+but they require frequent testing.
+Temperature-based methods, particularly body temperature tracking, offer a non-invasive alternative by
+detecting the slight temperature rise that follows ovulation.
+Advances in wearable technology have further enabled continuous and automated temperature monitoring,
+improving accessibility and usability\cite{alexander_fertilitatsmonitoring_2014, luo_detection_2020, yu_tracking_2022}.
+
+\subsection{Technical Background}\label{subsec:technological_background}